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vp16256 programmable fir filter advance information the vp16256 contains sixteen multiplier - accumulators, which can be multi cycled to provide from 16 to 128 stages of digital filtering. input data and coefficients are both represented by 16-bit twos complement numbers with coefficients converted internally to 12 bits and the results being accumulated up to 32 bits. in 16-tap mode the device samples data at the system clock rate of up to 40mhz. if a lower sample rate is acceptable then the number of stages can be increased in powers of two up to a maximum of 128. each time the number of stages is doubled, the sample clock rate must be halved with respect to the system clock. with 128 stages the sample clock is therefore one eighth of the system clock. in all speed modes devices can be cascaded to provide filters of any length, only limited by the possibility of accumulator overflow. the 32-bit results are passed between cascaded devices without any intermediate scaling and subsequent loss of precision. the device can be configured as either one long filter or two separate filters with half the number of taps in each. both networks can have independent inputs and outputs. both single and cascaded devices can be operated in decimate- by-two mode. the output rate is then half the input rate, but twice the number of stages are possible at a given sample rate. a single device with a 40mhz clock would then, for example, provide a 128-stage low pass filter, with a 10mhz input rate and 5mhz output rate. coefficients are stored internally and can be down loaded from a host system or an eprom. the latter requires no additional support, and is used in stand alone applications. a full set of coefficients is then automatically loaded at power on, or at the request of the system. a single eprom can be used to provide coefficients for up to 16 devices. pin 1 ident pin 208 pin 1 gh208 pin identification diagram (top view) see table 1 for pin descriptions and table 2 for pinout fig. 2 typical system application features n sixteen macs in a single device n basic mode is 16-tap filter at up to 40mhz sample rates n programmable to give up to 128 taps with sampling rates proportionally reducing to 5mhz n 16-bit data and 32-bit accumulators n can be configured as one long filter or two half- length filters n decimate-by-two option will double the filter length n coefficients supplied from a host system or a local eprom n 208-pin plastic powerquad pq2 package ordering information vp16256-27/cg/gh1n 27mhz, commercial plastic powerquad pq2 package (gh208) VP16256-40/cg/gh1n 40mhz, commercial plastic powerquad pq2 package (gh208) applications n high performance commercial digital filters n matrix multiplication n correlation n high performance adaptive filtering supersedes august 1997 version, ds4548 - 3.2 ds4548 - 4.0 august 1998 fig. 1 a dual filter application addr data eprom eprom gnd sclk res change coeff power-on reset vp 16256 output data input data addr data eprom gnd sclk res change coeff power-on reset vp 16256 output data adc coefficients eprom clkop analog input
2 vp16256 da15:0 16-bit data input bus to network a. db15:0 delayed data output bus in the single filter mode. connected to the data input bus of the next device in a cascaded chain. input to network b in the dual filter modes. x31:0 expansion input bus in the single filter mode. connected to the previous filter output in a cascaded chain. the inputs are not used on a single device system or on the termination device in a cascaded chain. the x bus provides the output from network b in both dual modes. f31:0 in single filter mode this bus holds the main device output. in dual mode it holds the output from network a. fen filter enable. the first high present on an sclk rising edge defines the first data sample. the control register and coefficient memory must be configured before fen is enabled. the signal must stay active whilst valid data is being received and must be low if frun is high. dfen delayed filter enable. this output is connected to the filter enable input of the next device in a cascaded chain when moving towards the termination device and with multiple stand-alone eprom-loaded configurations. it is used to coordinate the control logic within each device. swap selects either the upper or lower set of coefficients for bank swap. a low selects the lower bank, a high the upper bank. frun in eprom load mode, when high this signal allows continuous filter operations to occur without the need for the initial fen edge. if the device is not a single, interface or master device then this pin must be tied low. dclr a low on this signal on the sclk rising edge will clear all the internal accumulators. dclr need only remain low for a single cycle, signal busy will indicate when the internal clearing is complete. after a clear the device must be re-synchronised to the data stream using fen. it is recommended that fen is taken low at the same time as clear. fen may then be taken high to synchronise the data stream once busy has returned low. c15:0 16-bit coefficient input bus. in the byte mode of operation, c15:8 have alternative uses as explained in the text. a7:0 coefficient address bus. in the eprom mode a7:0 are address outputs for an eprom. in the remote host mode they are inputs from the host. a7 is not used when coefficients are loaded as 16-bit words. ccs this pin is similar in operation to a7:0 and provides a higher order address bit. when low the coefficients are loaded, when high the control register is loaded. wen in the remote mode this pin is an input which when low enables the load operation. in the eprom mode it is an output which provides the write enable for other slave devices. cs this pin is always an input and must also be low for the internal write operation to occur. byte when this pin is tied low, coefficients are loaded as two 8-bit bytes. when the pin is high they are loaded as 16-bit words. in the eprom mode this pin is ignored. eprom when this pin is tied low coefficients are loaded as bytes from an external eprom. the device outputs an address on a7:0. when the pin is high coefficients must be loaded from a remote master. they can then be transferred individually rather than as a complete set. sclk the main system clock; all operations are synchronous with this clock. the clock rate must be either 1, 2, 4, or 8 times the required data sampling rate. the factor used depends on the required filter length. clkop this output, when used to enable sclk, can provide a data sampling clock. it has the effect of dividing the sclk rate by 1, 2, 4 or 8 depending on the filter mode selected. oen tri-state enable for the f bus. when high the outputs will be high impedance. oen is registered onto the device and does not therefore take effect until the first sclk rising edge busy a high on this signal indicates that the device is completing internal operations and is not yet able to accept new data. the signal is used during automatic eprom loading, reset and accumulator clearing. res when this pin is low the control logic and accumulators are reset. in the eprom mode it will initiate a load sequence when it goes high. signal description table 1 pin descriptions notes 1. unused buses (e.g. x31:0 when the device is configured in single or termination mode) can be set to any value. they should ho wever be maintained at a valid logic level to avoid an increase in power consumption. 2. to ensure correct input voltage thresholds are maintained all the v dd and gnd pins must be connected to adequate power and ground planes.
3 vp16256 signal v dd f0 f1 gnd f2 f3 v dd f4 f5 gnd f6 f7 v dd f8 gnd f9 f10 v dd f11 f12 gnd f13 f14 f15 v dd f16 f17 gnd f18 f19 v dd f20 f21 f22 f23 v dd f24 f25 gnd f26 v dd f27 pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 signal f28 f29 gnd f30 f31 v dd fen dfen dclr gnd swap gnd oen clkop v dd da0 v dd da1 gnd da2 v dd da3 da4 v dd da5 gnd da6 da7 da8 da9 v dd da10 gnd da11 da12 da13 da14 v dd da15 gnd c0 c1 pin 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 signal gnd c2 v dd c3 c4 c5 c6 v dd c7 gnd c8 c9 c10 gnd c11 c12 c13 v dd c14 v dd c15 gnd gnd wen ccs cs v dd res gnd sclk gnd v dd byte eprom a0 v dd a1 gnd a2 a3 a4 v dd pin 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 signal a5 a6 gnd a7 db0 v dd db1 gnd db2 db3 db4 v dd db5 gnd db6 db7 v dd db8 v dd db9 db10 gnd db11 db12 v dd db13 db14 gnd db15 v dd gnd busy x0 v dd x1 gnd x2 v dd x3 x4 x5 x6 pin 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 signal gnd x7 x8 v dd x9 gnd x10 x11 x12 v dd x13 x14 gnd x15 x16 x17 v dd x18 gnd x19 x20 x21 v dd x22 gnd x23 x24 x25 x26 gnd x27 v dd x28 x29 x30 gnd x31 v dd frun gnd pin 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 table 2 vp16256 pinout (208-pin power pqfp - gh208)
4 vp16256 fig. 3 block diagram operational overview the vp16256 is an application specific fir filter for use in high performance digital signal processing systems. sampling rates can be up to 40mhz. the device provides the filter function without any software development, and the options are simply selected by loading a control register. the device can be user configured as either a single filter, or as two separate filters. the latter can provide two independent filters for the in-phase and quadrature channels after iq splitting, or can provide two filters in cascade for greater stop band rejection. the device operates from a system clock, with rates up to 40mhz. this clock must be 1, 2, 4, or 8 times the required sampling frequency, with the higher multiplication rates producing longer filter networks at the expense of lower sampling rates. devices can be connected in cascade to produce longer filter lengths. this can be accomplished without the need for any additional external data delays, and all the single device options remain available. continuous inputs are accepted, and continuous results produced after the internal pipeline delay. connection can be made directly to an a-d converter. the filter operation can be synchronised to a filter enable signal (fen) whose positive going edge marks the first data sample. the internal multiplier accumulator array can be cleared with a dedicated input. this is necessary if erroneous results obtained during the normal data flush through are not permissible in the system. coefficients can be loaded from a host system using a conventional peripheral interface and separate data bus. alternatively, they can be loaded as a complete set from a byte wide eprom. the device produces addresses for the eprom and a busy output indicates that the transfer is occurring. up to sixteen devices can have their coefficients supplied from a single eprom. these devices need not necessarily be part of the same filter network. each of the filter networks shown in fig. 3 contains eight systolic multiplier accumulator stages; an example with four stages is shown in fig. 4. input data flows through the delay lines and is presented for multiplication with the required coefficient. this is added to either the last result from this accumulator or the result from the previous accumulator. the filter results progress along the adders at the data sample rate. if the sample rate equals sclk divided by four, for example, then the accumulated result is passed onto the next stage every fourth cycle. the structure described is highly efficient when used to calculate filtered results from continuous input data. a comprehensive digital filter design program is available for pc compatible machines. this will optimise the filter coefficients for the filter type required and number of taps available at the selected sample rate within the vp16256 device. an eprom file can be automatically generated in motorola s-record format. swap a7:0 c15:0 ccs wen cs byte eprom fen dfen dclr res coefficient storage and control sclk frun clkop busy da15:0 f31:0 oen network a network b dual mode single mode mux db15:0 x31:0
5 vp16256 fig. 4 filter network diagram single filter options when operating as a single filter the device accepts data on the 16-bit da bus at the selected sample rate, see figs. 5 and 6. results are presented on the 32-bit f bus, which may be tristated using the oen input. signal oen is registered onto the device and does not therefore take effect until the first sclk rising edge. devices may be cascaded this allows filters with more taps than available from a single device. to accomplish this two further buses are utilised. the db bus presents the input data to the next device in cascade after the appropriate delay, while, partial results are accepted on the x bus. single filter mode is selected by setting control register bit 15 to a one. the required filter length is then selected using control register bits 14 and 13 as summarised in table 3. the options define the number of times each multiplier accumulator is used per sample clock period. this can be once, twice, four times, or eight times. in addition a normal/decimate bit (cr12) allows the filter length to be doubled at any sample rate. this is possible when the filter coefficients are selected to produce a low pass filter, since the filtered output would then not contain the higher frequency components present in the input. the nyquist criterion, specifying that the sampling rate must be at least double the highest frequency component, can still then be satisfied even though the sampling rate has been halved. the system clock latency for a single device is shown in table 3. this is defined as the delay from a particular data sample being available on the input pins to the first result including that input appearing on the output pins. it does not include the delay needed to gather n samples, for an n tap filter, before a mathematically correct result is obtained. cr input output filter setup 14 13 12 rate rate length latency 0 0 0 sclk sclk 16 taps 16 0 0 1 sclk sclk/2 32 taps 17 0 1 0 sclk/2 sclk/2 32 taps 16 0 1 1 sclk/2 sclk/4 64 taps 18 1 0 0 sclk/4 sclk/4 64 taps 20 1 0 1 sclk/4 sclk/8 128 taps 24 1 1 0 sclk/8 sclk/8 128 taps 24 table 3 single filter options fig. 5 single filter bus utilisation data delay line data out coeff ram adder z 2 1 data delay line coeff ram adder z 2 1 data delay line coeff ram adder z 2 1 data delay line coeff ram adder z 2 1 accumulate expansion in data in result out da15:0 f31:0 oen network a network b dual mode single mode mux db15:0 x31:0
6 vp16256 speed mode 0 (data input and output at f sclk ) cr14:13 = 00, cr12 = 0. clkop held high. 123 abc 16 17 18 a b c 31 32 33 a b c 34 35 d e sclk fen da15:0 f31:0 clkop speed mode 1 (data input and output at half f sclk ) cr14:13 = 01, cr12 = 0 123 ab 16 17 18 a b 78 79 80 a b c 81 82 sclk fen da15:0 f31:0 clkop first data point (a) is read on edge 1 first valid result including data point (a) available after edge 16 valid result contains the first 16 data points available after edge 31 first data point (a) is read on edge 1 first valid result including data point (a) available after edge 16 valid result contains the first 32 data points available after edge 78 speed mode 2 (data input and output at a quarter f sclk ) cr14:13 = 10, cr12 = 0 123 ab 20 21 22 a b 272 273 a b sclk fen da15:0 f31:0 clkop first data point (a) is read on edge 1 first valid result including data point (a) available after edge 20 valid result contains the first 64 data points available after edge 272 45 23 24 274 275 276 speed mode 3 (data input and output at an eighth f sclk ) cr14:13 = 11, cr12 = 0 123 a b 24 25 26 a b 1040 a sclk fen da15:0 f31:0 clkop first data point (a) is read on edge 1 first valid result including data point (a) available after edge 24 valid result contains the first 128 data points available after edge 1040 45 27 28 1041 1042 1043 6789 29 30 31 32 speed mode 1 decimating (data input at half f sclk and output at a quarter f sclk ) cr14:13 = 01, cr12 = 1. 123 ab 18 19 20 b 142 143 144 145 sclk fen da15:0 f31:0 clkop first data point (a) is read on edge 1 first valid result including data point (a) available after edge 18 valid result contains the first 64 data points available after edge 142 21 22 b fig. 6 single filter timing diagrams
7 vp16256 dual independent filter options when operating as two independent filters the device accepts 16 bit data on both the da and db buses at the selected sample rate, see fig. 7. results are available from both the f and x buses. the f bus may be tristated using the oen input. signal oen is registered onto the device and does not therefore take effect until the first sclk rising edge each filter must be configured in the same manner, and multiple device expansion is not possible due to the pin re- organization. the latter requirement can, of course, still be satisfied by several devices configured as single filters. dual independent filter mode is selected by setting control register bits 15 and 4 to a zero. the required filter length is selected using control register bits 14 and 13 as summarised in table 4, which also shows the resulting latency. as in single filter mode normal or decimate-by-two operation can be selected using control register bit 12. dual cascaded filter options when operating as two cascaded filters the device accepts 16 bit data on the da bus at the selected sample rate. results are presented on the 32-bit x bus, see fig. 8. each filter must be configured in the same manner. multiple device expansion is not possible in this mode. dual cascaded filter mode is selected by setting control register bit 15 to a zero and bit 4 to a one. the required filter length is selected using control register bits 14 and 13 as summarised in table 4, which also shows the resulting latency. the decimate-by-two option is not available in this mode. the data for the second filter network is extracted as the middle 16 bits from the first networks accumulated result. for successful operation the first filter network must have unity gain. see the section on filter accuracy for more details. the cascade option is used to increase the stop band rejection in a practical filter application. theoretically, increasing the number of taps in an fir filter will increase the stop band rejection, but this assumes floating point calculations with no accuracy limitations. in practice, with fixed point arithmetic, better performance is achieved with two smaller filters in series. cr input output filter setup 14 13 12 rate rate length latency ind cas 0 0 0 sclk sclk 8 taps 16 27 0 0 1 sclk sclk/2 16 taps 17 - 0 1 0 sclk/2 sclk/2 16 taps 16 28 0 1 1 sclk/2 sclk/4 32 taps 18 - 1 0 0 sclk/4 sclk/4 32 taps 20 36 1 0 1 sclk/4 sclk/8 64 taps 24 - 1 1 0 sclk/8 sclk/8 64 taps 24 40 table 4. dual filter options fig. 8 dual cascaded filter bus utilisation fig. 7 dual independent filter bus utilisation da15:0 f31:0 oen network a network b dual mode single mode mux db15:0 x31:0 da15:0 f31:0 oen network a network b dual mode single mode mux db15:0 x31:0
8 vp16256 filter accuracy input data and coefficients are both represented by 16-bit twos complement numbers. the coefficients are converted to twelve bits by rounding towards zero. this is achieved as follows. if the coefficient is positive then the least significant 4 bits are discarded. if the coefficient is negative then the logical or of the least significant 4 bits are added to the remainder of the word. twelve bit coefficients can be used directly provided the least significant four bits are set to zero. the fir filter results are calculated using a multiplier accumulator structure as shown in fig. 9. the truncation and word growth allowed for in the data path are explained in fig. 10. the 16-bit data and 12-bit coefficient inputs (each with one sign bit before the binary point), are presented to the multiplier. this produces a 28-bit result with two bits before the binary point. producing the full 28-bit result ensures that if both the data and coefficients are set to logic 1 a valid result is generated. prior to entering the accumulator the least significant 4 bits of the multiplier result are truncated and the resulting 24 bits sign extended to 32 bits. the final accumulator result is 32 bits with 10 bits before the binary point. thus 9 bits of word growth are allowed within the accumulator. all accumulator bits are made available on the output pins. in cascade mode the middle 16 bits from the network a accumulator are fed round to the network b data inputs, see fig. 10. coefficient adder input data accumulator result s 8 7 6 5 4 3 2 1 0 s s s s s s s s s 0 s 0 - 26 s s accumulator result these bits are passed to filter network b during cascade mode - 25 - 24 - 23 - 22 - 14 - 13 - 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 - 22 - 14 - 13 - 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 - 22 - 14 - 13 - 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 - 14 - 13 - 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 - 15 accumulator result multiplier result coefficient input data ? ? ? ? ? ? ? ? ? sign extended to 32 bits, least significant 4 bits truncated multiplication producing a 28-bit result fig. 10 filter accuracy fig. 9 multiplier accumulator
9 vp16256 cascading devices when the filter requirements are beyond the capabilities of a single device, it is possible to connect several devices in cascade increasing the number of taps available at the required sample rate. within each device all filter length, decimate, and bank swap options are still possible, but each device in the chain must be similarly programmed and configured as a single filter. the number of devices which can be cascaded is only limited by the possibility of overflow in the 32-bit intermediate accumulations. if more than sixteen devices are cascaded in auto eprom load mode, then an additional eprom will be needed. in modes where the data sample rate does not equal the clock rate. then the cascade arrangement shown in fig. 11 is used. delayed data is passed from device to device in one direction, while intermediate results flow in the opposite direction. the interface device both accepts the input data and produces the final result. it is not necessary for each device to know its exact position in the chain, but the device which receives the input data and produces the final result must be identified, as must the device which terminates the chain. the former is known as the interface device and the latter as the termination device, all others are intermediate devices. control register bits cr11:10 are used to define these positions as shown in table 6. the control logic in each of the devices must be synchronised with respect to the interface device. this is achieved by connecting the delayed filter enable output (dfen) to the filter enable input (fen) of the next device in the chain. the interface device, itself, needs a fen signal produced by the system, unless in eprom mode, where frun may be pulled high. even when the latter is true, the fen connection must be made between the remaining devices in the chain. by effectively extending the filter length, the cascade latency is therefore the same as for the single device in the same mode. once the pipeline is initially flushed the latency is as given in table 3. when devices are cascaded such that the data sample rate equals the clock rate, (control register bits 14:13 = 00), then a different cascade configuration must be used. this is shown in fig. 12. the number of devices that can be cascaded is, again, only limited by the 32-bit accumulators. in this mode the delayed data is passed from device to device in the same direction as the intermediate results. the device which accepts the input data is now at the opposite end of the chain to the device which produces the final result. the control logic in each of the devices must be synchronised this is achieved by connecting all the device fen inputs to the global fen. the cascade latency for the complete filter is built up from the 12 delays from the termination device, 8 delays from the interface device and additional intermediate devices each adding 4 delays. available options no more than 128 coefficients can be stored internally. this limits the filter length / decimate / bank swap options to those which do not require more than that number of coefficients. thus when a filter with 128 taps is to be implemented in a single device, it is not possible to decimate or bank swap. when a filter with 64 taps is implemented, decimate or bank swap are possible, but not both. with all other filter lengths, all decimate and bank swap configurations are possible. fig. 12 full speed cascaded system fig. 11 three-device cascaded system data in fen results out da15:0 fen f31:0 db15:0 dfen x31:0 interface device da15:0 fen f31:0 db15:0 dfen x31:0 intermediate device da15:0 fen f31:0 db15:0 dfen x31:0 termination device data in fen results out db15:0 fen f31:0 da15:0 dfen x31:0 interface device db15:0 fen f31:0 da15:0 dfen x31:0 intermediate device db15:0 fen f31:0 da15:0 dfen x31:0 termination device
10 vp16256 (a) single filters 32 31 0 127 not used 0 127 64 63 not used 0 127 32 31 64 63 16 tap 32 tap 64 tap no swap possible 0 127 128 tap 16 15 lower bank upper bank lower bank upper bank lower bank upper bank (b) dual filters b upper bank 32 31 0 127 not used 32 31 0 127 64 63 96 95 not used 48 47 0 127 16 15 32 31 64 63 8 tap 16 tap 32 tap filter b no swap possible filter a no swap possible 0 127 64 63 64 tap a lower b lower a upper b upper a upper bank b lower bank a lower bank a lower b lower a upper b upper fig. 13 coefficient memory map filter control two control modes are available selected by input signal frun. in eprom load mode, when frun is tied high the device will commence operation once the coefficients have been loaded. the clkop signal indicates when new input data is required and that new results are available, see fig. 6. in both eprom and remote master load modes, when frun is tied low filter operation will not commence until a high has been detected on signal fen. this mode allows synchronisation to an existing data stream. fen should be taken high when the first valid data sample is available so that both are read into the device on the next sclk rising edge.proper device operation requires fen to be low during control register and coefficient loading both in eprom mode and remote master mode. after loading coefficients, filter operation is determined by frun and fen as described above. during device reset res must be held low for a minimum of 16 sclk cycles. after a reset the control register returns to its default state of 8c80 hex . this places the device into the following mode : l single filter l sample rate equal to the clock rate l non-decimating l a single device (not in a cascade chain) l bank swap selected by bit in the control register coefficient bank swap a bank swap feature is provided which allows all coefficients to be simultaneously replaced with a different set. a bit in the control register (cr7) allows the swap to be controlled by either input signal swap or control register bit (cr6). the latter is useful if the device is controlled by a microprocessor, when driving a separate pin would entail additional address decoding logic and an external latch. if swap or bit cr6 is low, the coefficients used will be those loaded into the lower banks illustrated in fig. 13. when the swap or cr6 is high, the upper banks are used. the actual swap will occur when the next sampling clock active going transition occurs. this can be up to seven system clocks later than the swap transition, and is filter length dependent. the first valid filtered output will then occur after the pipeline latencies given in tables 3 and 4. by setting a bit in the control register it is possible to bank
11 vp16256 swap on every data sampling clock. this function does not depend on the status of swap or bit, and the lower bank will be initially selected after fen goes active. the option can be used to implement filters with complex coefficients. loading coefficients when the device is to operate in a stand alone application then the coefficients can be down loaded as a complete set from a previously programmed eprom. alternatively if the system contains a microprocessor they can be individually transferred from a remote master under software control. in any mode the system clock must be present and stable during the transfer, and the addressing scheme is such that the least significant address specifies the coefficient applied to the first multiplier seen by incoming data. the addresses used during the load operation are those illustrated in fig. 13. the control register is loaded when ccs is high. in byte mode address a0 is used to select the portion of control register loaded, otherwise the address bits are redundant. when an eprom is used to provide coefficients, this redundancy causes the number of locations needed for any device to be double that for the coefficients alone. auto eprom load when eprom is tied low, the vp16256 assumes the role of a master device in the system and controls the loading of coefficients from an external eprom, see fig.15. a load sequence commences when the res input goes high, and will continue until every coefficient has been loaded. busy goes high to indicate that a load sequence is occurring and the filter output is invalid. the device will not commence a filter operation until the fen edge is received after busy has gone low. this requirement can be avoided if frun is tied high. the address bus pins become outputs on the master device, and produce a new address every four system clock periods. this four clock interval, minus output delays and the data set up time, defines the available eprom access time. the coefficients are always loaded as bytes. the state of the byte pin on the master device is ignored. this arrangement also allows the eight most significant coefficient bus pins (c15:8) to be used for other purposes as described later. since the 16-bit coefficients are loaded in two bytes the a0 pin specifies the required byte. the maximum number of stored coefficients is 128, eight address outputs are therefore provided for the eprom. these eight outputs from the master must also drive the address inputs on the slave devices. load last master coefficient sclk a7:0 ccs c15:12 fe ff 00 01 00 01 fe ff 00 01 00 01 0000 0001 0001 0010 load slave 1 control register load slave 1 coefficients load last slave 1 coefficient load slave 2 control register load slave 2 coefficients fig. 14a eprom load sequence fig. 14b eprom load sequence for a cascaded system sclk 00 01 00 load master control register load last coefficient a7:0 00 01 load first coefficient valid addr valid addr ccs res busy fig. 14 eprom load sequence timing diagrams
12 vp16256 when the filter length is less than the maximum, the vp16256 will only transfer the correct number of coefficients, and one or more significant address bits will remain low. sufficient coefficients are always loaded to allow for a possible bank swap to occur, and the eprom allocation must allow for this even if the feature is not to be used. table 5 shows the number of coefficients loaded for each of the modes. if several devices are cascaded, only one device assumes the role of the master by having its eprom pin grounded. it produces a wen signal for the other devices, plus four higher order address outputs on c15:12, see fig. 14. the extra address bits on c15:12 define separate areas of eprom, containing coefficients for up to fifteen additional devices. the least significant block of memory must always be allocated to the master device. the additional devices need not in practice be all part of the same cascaded chain, but can consist of several independent filters. they must, however, all have their byte pins tied low. frun can still be used to start these independent filters after all the devices have been loaded. in this case, however, each slave fen pin should be driven by dfen from the master device. when one eprom is supplying information for several devices, some means of selectively enabling each additional device must be provided. this is achieved by using the c11:8 pins on the slave devices as binary coded inputs to define one to fifteen extra devices. these coded inputs always fig. 15 three device auto eprom load correspond to the block address used for the segment of eprom allocated to that device. code all zeros must not be used since the master device has implied use of the bottom segment. this is necessary since the c11:8 pins are alternatively used on the master device to define the number of devices supported by the eprom. in addition to providing the most significant addresses to the eprom, the c15:12 address outputs from the master device must also drive the c15:12 inputs on the slave devices. these c15:12 inputs are internally compared to the c11:8 inputs to decide if that device is currently to be loaded. this approach avoids the need for external decoders and makes the cs input redundant. this input, however, must be tied low on every device in an eprom supported system. the control coefficient pin (ccs) is used to define when the control register is to be loaded. it becomes an output on the master device which provides an eprom address bit next in significance above a7:0, and also drives the ccs inputs on the slave devices. this output is high for the first two eprom transfers in order to access the control information, and then remains low whilst the coefficients are loaded. this control information is thus not stored adjacent to the coefficients within the eprom, and in fact the eprom must provide twice the storage necessary to contain the coefficients alone. all but two of the bytes in the additional half are redundant. see fig.16 for the eprom memory map. c11:8 cs eprom byte wen a7:0 ccs c15:12 c7:0 0010 gnd gnd gnd (2 slaves) master c11:8 cs eprom byte wen a7:0 ccs c15:12 c7:0 0001 gnd v dd gnd slave 1 c11:8 cs eprom byte wen a7:0 ccs c15:12 c7:0 0010 gnd v dd gnd slave 2 lsb msb data address ? ? ? eprom vp16256 vp16256 vp16256
13 vp16256 using a remote master when a remote master is used to load coefficients, eprom must be tied high and a conventional peripheral interface is then provided. it is not possible, however, to read coefficients already stored. the master supplies an address and data bus, and writes to the vp16256 occur under the control of synchronous cs and wen inputs. the coefficient control register pin (ccs) must be driven by a master address line higher in significance than a7:0. both the wen and cs signals must be low for the load operation to occur. when loading the control register the cs signal must be held low for a further 2 cycles, see fig. 19. since the internal write operation is actually performed with the system clock, it is necessary for the clock to be present during the transfer. the byte input defines whether coefficients are loaded as a single 16 bit word or two 8-bit bytes. the latter saves on connections to the remote master. address bits a7:0 are used in byte mode. 16-bit word mode uses bits a6:0, a7 being redundant. when writing in byte mode the least significant byte (a0 = 0) must be written first followed by the most significant byte (a0 = 1). in byte mode the internal comparison between c15:12 and c11:8 is made, regardless of the state of eprom. for this reason pins c15:8 should all be tied low when a remote master is used with byte transfers. this ensures that the internal comparison gives equality and allows the load operation to occur. the address and coefficient buses plus the wen and cs signals must all meet the specified set up and hold times with respect to the system clock, see fig 19 and switching characteristics. this synchronous interface is optimum for the majority of high end applications, when individual coefficients must be updated at sample clock rates. however, if the coefficients are to be loaded under software control from a general purpose microprocessor, the processors write strobe will probably be asynchronous with the sclk clock used by the vp16256. in this case external synchronising logic is needed, as shown in fig.17. fig. 18 shows the recommended loading sequence and filter operation initiation. the simplest technique is to reset the device prior to loading a set of coefficients. coefficients may be loaded once busy returns low or 22 cycles after res is taken high. when loading a device from a remote master the control register must be loaded first followed by the filter coefficients. fig. 18 shows the required loading sequence, two examples are given one for byte mode the other for word mode. a gap of at least one cycle must be left after loading the control register before loading the first coefficient. filter operations are started by presenting the first data word at the same time as raising signal fen; frun should always be low. fig. 16 eprom memory map note: the eprom memory map assumes that, for the 32 and 64 coefficient per device options, the unused address pins are unconnected. if all address pins are connected as shown in fig. 15 then the 128 coefficients per device memory map column should be used. only those coefficients required will be read, hence the upper portions of the coefficient address space will be ignored. table 5. number of coefficients loaded control number of register coefficients loaded 14 13 12 000 32 001 64 010 64 0 1 1 128 1 0 0 128 1 0 1 128 1 1 0 128 1 1 1 invalid mode 1023 770 769 768 767 512 511 258 257 256 255 0 filter coefficients not used control reg 511 386 385 384 383 256 255 130 129 128 127 0 255 194 193 192 191 128 127 66 65 64 63 0 not used control reg filter coefficients coefficients per device 32 64 128 ? ? ? ? ? ? ? ? ? ? ? ? ? ? device 2 device 1
14 vp16256 fig. 17 remote master synchronisation sclk wen vp 16256 processor write strobe dq coefficient load state machine hold circuit address data a7:0 c15:0 sclk address/data registered strobe address and data valid vp16256 wen a7:0 and c15:0 held after falling edge of write strobe a7:0/c15:0 strobe registered into synchronisation register strobe registered into state machine coefficient input clocked to vp16256 on this edge processor write strobe
15 vp16256 res must be held low for 16 cycles busy goes active coefficient loading may start once busy has returned low 1234567 1617 373839 device reset sclk res busy 1234567 byte wide coefficient load 8 67 68 69 70 71 00 01 00 01 02 03 3e 3f 00 ac 10 00 20 00 00 02 control register loaded with ccs high blank cycles coefficients loaded into the required address location. this example uses byte wide loading ( byte held low). cs must be maintained for two cycles sclk ccs a7:0 c15:0 cs wen control register loaded with ccs high blank cycles coefficients loaded into the required address location. this example uses word wide loading ( byte held high). wen 1234567 word wide coefficient load 8 34 35 36 37 38 00 01 02 03 1e 1f ac00 0020 0030 0040 0050 001f 0200 sclk ccs a7:0 c15:0 cs 00 0010 04 1234567 start of filter operation 8 9161718 19 0010 0000 0090 0001 sclk fen da15:0 f31:0 clkop 0020 0030 0040 0050 00a0 0001 0004 0004 0000 0000 0000 0000 0000 0000 0000 0000 0000 the first data sample is read as fen goes high the first result available. clkop indicates the first active result cycle fig. 18 device startup timing diagrams
16 vp16256 control register the internal operation of the vp16256 is controlled by the status of a 16-bit control register. in the dual filter modes both networks are controlled by the same register. the significance of the various bits are shown in table 6. tables 7 and 8 define the control register bit interdependence for the filter and bank swapping modes. the control register is double buffered. this allows the writing of a new control word without affecting the current operation of the device. to activate the new control register after it has been written to the device the bank swap signal must be toggled. after a reset the active control register is loaded directly and bank swap need not be used. control register function bits 765 0 x 0 control by input pin 1 0 0 lower bank selected 1 1 0 upper bank selected x x 1 swap on every sample clock table 8 control register bank swap bits bits decode function 15 0 dual filter mode 15 1 single filter mode 14:13 00 sample rate is the system clock 14:13 01 sample rate is half the system clock 14:13 10 sample rate is quarter the system clock 14:13 11 sample rate is eighth the system clock 12 0 output rate equals the input rate 12 1 decimate-by-two 11:10 00 intermediate device 11:10 01 interface device 11:10 10 termination device 11:10 11 single device 9:8 00 these bits must be at logical zero 7 0 bank swap is controlled by input pin 7 1 bank swap is controlled by bit 6 6 0 lower bank if bit 7 is set 6 1 upper bank if bit 7 is set 5 0 normal bank swap 5 1 bank swap on every sample clock 4 0 two independent filters 4 1 two filters in cascade 3:0 these bits must be at logical zero control register function bits 15 4 0 0 two independent filters 0 1 two filters in cascade 1 x single filter table 7 control register filter mode bits absolute maximum ratings (note 1) supply voltage v dd 2 05v to 1 70v input voltage v in 2 05v to v dd 1 05v output voltage v out 2 05v to v dd 1 05v clamp diode current per pin i k (see note 2) 18ma static discharge voltage (hbm) 500v storage temperature t s 2 65 c to 1 150 c ambient temperature with power applied t amb 0 c to 1 70 c junction temperature with power applied t j 120 c package power dissipation 2500mw thermal resistance, junction-to-case q jc 10 c/w notes 1. exceeding these ratings may cause permanent damage. functional operation under these conditions is not implied. 2. maximum dissipation should not be exceeded for more than1 second, only one output to be tested at any one time. 3. exposure to absolute maximum ratings for extended periods may affect device reliablity. 4. current is defined as negative into the device. 5. the q jc data assumes that heat is extracted from the bottom of the package via the integral heat sink. 6. the metal heat slug in the base of the package is connected to the substrate, which is at v dd potential. table 6 control register bit allocation
17 vp16256 fig. 19 remote master setup and hold timings fig. 20 eprom load timings fig. 21 operating timings sclk a7:0 ccs c15:0 valid data cs wen valid address (a) coefficient write t hs t hh sclk a7:0 ccs c15:0 cs wen t hs t hh valid data valid address (b) control register write t cl t ch t hh sclk c15:12 a7:0 ccs valid address c7:0 t cd t hs t hh ~ ~ ~ ~ ~ ~ t cd clk 1 clk 2 clk 9 ~ ~ ~ ~ ~ ~ valid address ~ ~ ~ ~ sclk f31:0 oen output pins valid data high z valid data valid data valid data valid data input pins t os t cd t cl t ch t czf t cvf t hs t hh t oh
18 vp16256 electrical characteristics the electrical characteristics are guaranteed over the following range of operating conditions, unless otherwise stated: t amb = 0 c to 1 70 c, t j = 1 120 c, v dd = 1 5v 10%, gnd = 0v static characteristics min. typ. max. output high voltage output low voltage input high voltage (cmos) input low voltage (cmos) input high voltage (ttl) input low voltage (ttl) input leakage current input capacitance output leakage current output short circuit current 10 - 04 - 10 - 08 1 10 1 50 300 24 - 35 - 20 - 2 10 2 50 10 v oh v ol v ih v il v ih v il i in c in i oz i os i oh = 4ma i oh = 4ma sclk input only sclk input only all other inputs all other inputs gnd < v in < v dd gnd < v out < v dd v dd = 1 55v v v v v v v m a pf m a ma units value conditions characteristic symbol min. typ. max. min. typ. max. input signal setup to clock rising edge input signal hold after clock rising edge oen set up to clock rising edge oen hold after clock rising edge clock rising edge to output signal valid clock frequency clock high time clock low time clock to data valid f bus from high impedance clock to data high impedance f bus v dd current ns ns ns ns ns mhz ns ns ns ns ma 290 - - - - 18 27 - - 35 35 325 8 0 20 4 5 - 14 14 - - t hs t hh t os t oh t cd f sclk t ch t cl t cvf t czf i dd 395 - - - - 17 40 - - 23 23 450 7 0 20 4 5 - 10 10 - - 30pf see fig. 22 see fig. 22 see note 1 note 1. v dd = 1 55v, outputs unloaded, clock frequency = max. vp16256-27 VP16256-40 conditions units characteristic symbol switching characteristics (see figs. 19, 20 and 21) fig. 22 three state delay measurement v h 05v delay from output high to output high impedance 05v 05v 05v v l 15v 15v delay from output low to output high impedance delay from output high impedance to output low delay from output high impedance to output high test waveform measurement level v h is the voltage reached when the output is driven high vl is the voltage reached when the output is driven low i ol 15v i oh dut 30pf three state delay measurement load

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