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june 2006 rev 1 1/23 AN2038 application note i2c emulation with st7mc in slave mode 1 introduction this application note describes how to emulate i2c communication using an st7mc as slave device. since there is no dedicated i2c pe ripheral in the st7mc microcontroller, the protocol is emulated using the spi peripheral. this peripheral is common to different st7 products so the software presented can be easily adapted to run in other st7 microcontrollers. in this document, the hardware and software description refers to the st7mc microcontroller for moto r control applications. see section 7: reference and related materials to get more information about standard motor control libraries. section 4: software modifications describes the modification you need to make to implement i2c communication in the current standard libraries for specific types of motor. section 3: hardware modifications describes the required modifications to the st7mc starter kit board (softec ak-st7fmc) for implementing i2c communication. the two modules presented in this application note are c modules (.h and .c file) developed to be compiled with cosmic compiler v.4.5b (see www.cosmic-software.com for information and free download) and used in softec stvd7 v.3.10 integrated development environment (see www.softecmicro.com for information and free download). the first module, called i2c module implements the low level i2c protocol, the second module, called protosup module is an example of a customized protocol based on i2c emulation. this protocol implements a frame of communication that allows the master to send a set of typical commands for a motor control application. you should have a basic knowledge of c programming, motor control drives and basics of i2c protocol in order to use this module. in-depth know-how of st7mc functions is only required for customizing existing modules or when adding new modules to develop your own application. www.st.com
contents AN2038 2/23 contents 1 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 i2c emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 i2c basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 i2c architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 i2c emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 hardware modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 software modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1 standard motor control libraries for st7mc starter kit . . . . . . . . . . . . . . . 9 5 command frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6 function description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1 i2c module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2 protosup module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7 reference and related materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
AN2038 i2c emulation 3/23 2 i2c emulation 2.1 i2c basics the i2c-bus has two wires, serial data (sda) and serial clock (scl), used to carry information between the devices. each device is recognized by a unique address and can operate as either a transmitter or receiver , depending on the function of the device. in addition to transmitters and receivers, devices can also be considered "masters" or "slaves" when performing data transfers. a master is the device which initiates a data transfer on the bus and generates the clock signals. at that time, any device addressed is considered a slave. both sda and scl are bi-directional lines, connected to a positive supply voltage via a pull- up resistor (see figure 1 ). when the bus is free, both lines are high. the output stages of devices connected to the bus must have an open-drain or open-collector to perform the and function. since data on the i2c-bus can be transferred at rates more than 100 kb/s in standard-mode, in this application we reach a speed of 4 kb/s. this is caused by need to emulate the i2c with the spi peripheral and the presence of a non-interruptible interrupt sub-routine for the motor control application. figure 1. i2c bus the data on the sda line must be stable during the high period of the clock. the high or low state of the data line can only change when the clock signal on the scl line is low (see figure 2 ). figure 2. data valid +vdd sda scl sda scl sda scl r p r p dev1 dev2 data stable changing allowed data stable sda scl
i2c emulation AN2038 4/23 a high to low transition on the sda line while scl is high indicates a start condition. a low to high transition on the sda line while scl is high indicates a stop condition (see figure 3 ). start and stop conditions are always generated by the master. the bus is considered to be busy after the start condition. the bus is considered to be free again after the stop condition. figure 3. start/stop condition every byte put on the sda line must be 8 bits long. the number of bytes that can be transmitted per transfer is unrestricted. each byte has to be followed by an acknowledge bit. data is transferred with the most significant bit (msb) first (see figure 4 ). figure 4. data transfer the acknowledge clock pulse is generated by the master. the transmitter releases the sda line (high) during the acknowledge clock pulse and the receiver must pull down the sda line during the acknowledge clock pulse so that it remains stable low during the high period of this clock pulse. data transfers follow the format shown in figure 5 : after the start condition (s), a slave address is sent. this address is 7 bits long followed by an eighth bit which is a data direction bit (r/w) - a 'zero' indicates a transmission (write), a 'one' indicates a request for data (read). a data transfer is always terminated by a stop condition (p) generated by the master. stop start scl sda 12 78 12 7 8 msb lsb msb lsb start stop ack ack sda scl first byte second byte
AN2038 i2c emulation 5/23 figure 5. 7-bit addressing possible data transfer formats are: master-transmitter transmits to slave-receiver. the transfer direction is not changed (see figure 5 "master transmit bytes to slave"). master reads slave immediately after first byte (see figure 5 "master receive bytes from slave"). at the moment of the first acknowledge, the master transmitter becomes a master-receiver and the slave-receiver becomes a slave-transmitter. this first acknowledge is still generated by the slave. the stop condition is generated by the master. see figure 6 for the format of first byte after the start condition. figure 6. first byte after the start condition 2.2 i2c architecture in figure 7 shows the hardware architecture used to implement i2c emulation using the spi peripheral. the st7mc is connected to the i2c bus through an optoisolator able to isolate the high voltage section from the bus. by means of one i/o pin the st7mc is able to select if the spi bus is used in i2c emulation mode or in spi mode for communication with the spi memory. in the first case the optoisolator is enabled and the spi memory is disabled, in the second case the optoisolator is disabled so spi and i2c are unconnected and spi memory is enabled. slave address s r/w a data a data a p slave address s r/w a data a data a p master transmits bytes to slave master receives bytes from slave from master to slave from slave to master ?0? ?1? s: start p: stop a: acknowledge slave address msb lsb r/w
i2c emulation AN2038 6/23 figure 7. hardware architecture the mosi and miso pins are unidirectional lines, the first from master to slave and the second from slave to master. both are connected together after the optoisolator to become the sda bidirectional line. the sck line is driven by the master and is connected to scl. two i/o interrupts are used to sense the edge of the sda and scl signal and to signal the various i2c events (start condition, stop condition, acknowledge) to the microcontroller. 2.3 i2c emulation when emulating the i2c bus using spi it is important to manage the following conditions: detection of start condition validation of start condition end of byte receive (spi) end of byte transmission (spi) validation of the transmission detecting a master acknowledge time out detection of the stop condition the detection of the start condition is performed using an interrupt port sensitive to the falling edge of the sda signal. each time a fa lling of sda occurs to gether with scl in high state, a start condition occurs. a state machine is implemented to manage the start condition. the state machine has the following states: mosi miso sck mosi miso sck sda scl opto-isolation spi memory st7mc i/o pin interrupts i/o cs cs i 2 c table 1. start condition management state description wait_start in this state the micro is waiting fo r a start condition. after a falling edge occurs on sda when scl is high, the state is changed to start_validation start_validation in this state the micro is in waiting for a validation of start condition. the start condition is validated when the first faling edge on scl occurs, in this case the state is changed to communication communication in this state the micr o is exchanging data using the spi
AN2038 i2c emulation 7/23 if a timeout occurs or a stop condition is detected the state is forced to wait_start. each time a rising edge occurs on sda occurs together with scl in high state, a stop condition occurs. in this case a flag is set indicating that new data has been received or transmitted. this flag is used by the protosup module. when an spi interrupt occurs a byte is received or transmitted. if it is the first byte after the start condi tion, this byte will be analyzed to see if: the slave is addressed, this is the case if the address of the slave is equal to the microcontroller i2c address. if the transmission is a write from the master or a read from the slave. if it is the former, the following bytes have to be read else the transmission buffer has to be transmitted using spi. the corresponding status flag is therefore set. if the byte received is not the first byte, it is stored in a read buffer. if an end of transmission interrupt occurs, the microcontroller has to validate the transmission by detecting the master acknowledge. the detection of master acknow ledges will be performed in the scl interrupt service routine on falling edge. after the detection of the master acknowledge a new byte in the transmission buffer will be sent. if the buffer is empty, the condition is indicated setting a flag.
hardware modifications AN2038 8/23 3 hardware modifications the following modifications should be performed on the softec starter kit to allow the i2c emulation. figure 8 shows the i2c module board with the required optical isolation. j1 is the connector interface to the i2c bus and j2 is the connector interface to the st7mc starter kit. to use the module you must connect j2 to the starter kit pins. since there is no free available pin on the board, you have to to solder the wires directly to the pins listed in ta bl e 2 . note: u10 is the st7mc2 chip. figure 8. i2c module schematic table 2. hardware j2 connection to be soldered in st7mc starter kit j2 pin starter kit j2 pin starter kit j2 pin starter kit 1 u10 pin 41 3 u10 pin 20 4 u10 pin 30 5 u10 pin 27 6 u10 pin 25 7 u10 pin 26 8 u10 pin 47 10 u10 pin 40 5 5 4 4 3 3 2 2 1 1 d d c c b b a a sda gnd gnd (micro) mosi int sda (pd1) +5v (micro) int sck (pc1) i2c enable (pa6) miso sck sck 1.0 i2cbd 11 wednesday, april 05, 2006 title size document number rev date: sheet of +5 +5 ns ns +5 miso +5 +5 +5 +5 ns ns +5 miso +5 ck +5 +5 +5 mosi +5 r1 390 sfh615a 3 1 2 4 q4 bc557 sfh615a 3 1 2 4 r3 1.8k r4 3.9k r14 6.8k u4 nme0505s 1 2 4 3 gnd vin vo 0v c3 100nf 25v c2 1uf 16v sfh615a 3 1 2 4 r6 100 r15 10k r2 680 q1 bc547 q3 bc547 q2 bc547 r9 6.8k r8 6.8k r7 6.8k r10 10k r11 10k r12 10k r13 5.6k j1 con3 1 2 3 j2 con10 1 2 3 4 5 6 7 8 9 10
AN2038 software modifications 9/23 4 software modifications to implement the i2c emulation you have to perform the following modifications to the standard motor control software library. 4.1 standard motor control libraries for st7mc starter kit at the moment the following standard libraries are released for the st7mc starter kit (motor control application), each dedicated to specific kinds of motor. the libraries are listed in ta bl e 3 . see section 7: reference and related materials for details on the motor control libraries. table 3. motor control standard libraries library name description ac_1ph_sr_2.0 induction mono phase motors sensored ac_2ph_sr_2.0 induction bi phases motors sensored ac_3ph_sr_2.0 induction three phases motor sensored bldc_3ph_sl_2.0 brushless or permanent magnet motors drive in trapezoidal mode (6 step) sensorless bldc_3ph_sr_2.0 brushless or permanent magnet motors drive in trapezoidal mode (6 step) sensored pmac_3ph_sr_2.0 brushless or permanent magnet motors drive in sinusoidal mode sensored
software modifications AN2038 10/23 the following steps are required to modify the standard libraries to emulate the i2c using spi: first, configure the libraries using the configuration tools ak-st7fmc control panel. refer to the related manual. copy the two provided modules (i2c.c, i2c.h, protosup.c, protosup.h) in the project folder. copy the vector.c file provided into the project folder overwriting old vector.c file. copy the main.c file provided into the pr oject folder overwriting old main.c file. open the workspace using softec stvd7 v.3.10 integrated development environment. add the two files i2c.c and protosup.c in the "source files" folder of the workspace and the two files i2c.h and protosup.c in the "include files" folder of the workspace. inside the i2c.h file select the kind of motor defining the corr espondent motor_type constant pmac, bldc or ac: #define motor_type pmac or #define motor_type bldc or #define motor_type ac interrupt priority setup: if the ac (or pmac) motor has been selected, then modify the st7_intprioritysetup function defined in the st7_misc.c file: ispr0 = mces_lvl_3 + mcc_si_lvl_1 + ext_it0_lvl_2 + ext_it1_lvl_1; ispr1 = ext_it2_lvl_2 + mtc_u_cl_so_lvl_3 + mtc_r_z_lvl_2 + mtc_c_d_lvl_2; ispr2 = spi_lvl_2 + timer_a_lvl_2 + timer_b_lvl_1 + sci_lvl_1; if the bldc motor has been selected, then modify the st7_intprioritysetup function defined in the misc.c file: itspr0 = mces_lvl_3 + mcc_si_lvl_1 + ext_it0_lvl_2 + ext_it1_lvl_1; itspr1 = ext_it2_lvl_2 + mtc_u_cl_so_lvl_3 + mtc_r_z_lvl_3 + mtc_c_d_lvl_3; itspr2 = spi_lvl_2 + timer_a_lvl_2 + timer_b_lvl_3 + sci_lvl_1; itspr3 = (avd_lvl_1 + pwmart_lvl_2) | (u8)(0xf0); modification related to pmac motor modify the pmacparam.h: modify the define of target frequency #define target_freq_cl 1500 in extern u16 target_freq_cl;
AN2038 software modifications 11/23 modification related to bldc motor modify the mtc.h: #define motorstalled 4 inside the mtc.c for bldc motor ? add the following include at the beginning #include "i2c.h" #include "protosup.h" ? then is necessary to modify the chk_motor_stalled() and mtc_c_d_it() functions to manage the fault condition. inside chk_motor_stalled() function add the following // frequency synchronization if ((mprsr & 0x0f) == ratio_max) { command = cmd_brake; motorstatus = motor_stalled; ?. } only for bldc sensorless, inside mtc_c_d_it () function find the following block and modify as written. if (rampindex >= (ramp_size-1))// if ramp is finished without success { ??.. motorstatus |= start_up_failed; command = cmd_brake; ???. }
command frames AN2038 12/23 5 command frames the commands are sent from the master to the slave and are organized as shown in figure 9 . after the start condition, the first byte addresses the slave and forces a w to send the command to the slave. stx is a byte that indicates a start of transmission and is coded in table 4. then is dispatched a byte with the length (n ) of the sequence of by tes that will be sent. d1 is the "command" byte see table 4. d2 - dn is an optional se quence of bytes; this is a additional parameter sent together with the command. the next two bytes crc1 and crc2 is the checksum calculated wi th the following rule: crc calculation crc value is a 16-bit value that contains the sum of d1, d2, ? , dn. crc 1 is the msb of crc value. crc 2 is the lsb of crc value. the last byte is etx that indicates the end of transmission. figure 9. communication frame (command from master) as command the master can ask a request from the slave. the next frame is organized as show in figure 10 . after the ask command of the previous frame the master start a new communication and in the first byte after the start condition it address the slave from which it wait the answer and force a r. the slave sent the following byte: stx is a byte that indicates a start of transmission and is coded in the ta bl e 4 . after that it is transmitted a byte with the le ngth (n) of the se quence of bytes that will be sent. d 1 - d n is the answer from the slave. the next two byte crc 1 and crc 2 is the checksum calculated with the above described rule. the last byte is etx that indicate the end of transmission. stx length = n d 1 d 2 d n ? crc 1 crc 2 etx command parameters from master
AN2038 command frames 13/23 figure 10. communication frame (response from slave) motor status byte ms: motor stalled sf: startup fails ot: over temperature ov: over voltage oc: over current table 4. i2c code table communication code stx 0x02 start transmission etx 0x03 end transmission ack 0x1c acknowledge not_ack 0xee not acknowledge not_ready 0xcc not ready wait 0xfc wait master commands cmd_setspeed 0x77 command set speed. d2 and d3 will be respectively msb and lsb of a word contains speed in rpm. cmd_brake 0x88 command brake cmd_start 0x66 command start motor master query ask_status 0x08 master asks for motor status . d1 and d2 of subsequent answer of the slave is a byte formatted as below. d2 is a checksum byte equal to complemented bit respect d1 ask_speed 0x07 master asks for motor speed. d1, d2, d3, d4 of subsequent answer of the slave is respectively msb and lsb of a word contains speed in rpm. d3 and d4 is two checksum byte equal to complemented bit respect d1 and d2 000mssfovocot slave addr. + r stx length = n d 1 d 2 d n ? crc 1 crc 2 etx answer from slave from slave from master
function description AN2038 14/23 6 function description the two i2c modules are organized as shown in figure 11 . i2c module function is to get or put the raw data from/to the i2c bus into two data buffer i2c_data_r and i2c_data_w. protosup module function is to extract the valid data from the stream coming from i2c_data_r buffer into the valid_data_in and from valid_data_out buffer into i2c_data_w buffer. figure 11. firmware architecture protosup module link protocol i2c_data_r i2c_data_w valid_data_in valid_data_out i 2 c module i 2 c bus
AN2038 function description 15/23 6.1 i2c module this module contains the low level routine to emulate the i2c communication protocol. initialization routine function name input parameter return value init_i2c_protocol void void description i2c module initialization. this function should be called inside the main, before the main loop, to initialize the i2c emulation. this function calls the following initialization function: ? init_spi_4_i2c ? init_timer_4_i2c ? init_int_sck_4_i2c ? init_int_sda_4_i2c this function also set the status of the i2c state machine to wait_s tart, it means that the micro is in waiting of a start condition. the i2c slave acknowledge flag is set false (no ack from slave in progress). this function also set the pa6 as output push pull and with an high value to select spi bus for i2c communication. function name input parameter return value init_spi_4_i2c void void description spi peripheral initialization. (this function is called by init_i2c_protocol) this function performs first the in itialization of the i/o of spi pins calling "init_spi_ports" routine. then it clears the contingent pending spi interrupt. then enable spi interrupt, disable alternate function that will be enabled further, sets spi clock edge as rising edge and sets the slave mode. function name input parameter return value init_timer_4_i2c void void description timer (a) initialization. (this function is called by init_i2c_protocol) initialization of timer a used for time out purpose. timeout defines the number of micr oseconds it is defined in i2c.h. the timer is freeze and will be started using start timer when the start condition occurs. after the time out the isr "timer_a_interrupt_routine" will be served.
function description AN2038 16/23 low level routine function name input parameter return value init_int_sck_4_i2c void void description initialize the external interrupt sck (ei2 pc1) . (this function is called by init_i2c_protocol) this function sets pc1 as floating interrupt sensitive to falling edge. function name input parameter return value init_int_sda_4_i2c void void description initialize the external interrupt sda (ei0 pd1) . (this function is called by init_i2c_protocol) this function sets pd1 as floating interrupt sensitive to rising and falling edge. function name input parameter return value i2c_enable_spi void void description this function enables the spi communication. it is ena bled after a start condition and falling of sck. it clear also the pending bit. function name input parameter return value i2c_disable_spi void void description this function disables the spi communication. t he ports is dedicated to s ensing the edge transition using port interrupts. function name input parameter return value i2c_stop_detected void void description this function is called when a stop condition is detected. it disables the spi peripheral and reinitialize sda and sck interrupts. if the communication is from master to slave (i2c_slave_read_flag set true) the flag new_data_receved is set to true for high level protocol purposes (protosup), otherwise if the communication is from slave to master (i2c_slave_write_flag set true) the flag new_data_sent is set to true.
AN2038 function description 17/23 interrupt service routine function name input parameter return value reset_timer void void description reset and freeze the timer. it is called after a validation of start condition. function name input parameter return value start_timer void void description unfreeze the timer. it is called when a falling of sda occurs when scl is high (start condition) function name input parameter return value timer_a_interrupt_routine void void description timeout interrupt service routine. it is used to reset the state if a start condition is not validated. the isr will be executed timeout microseconds (defined in i2c.h) after the "start_timer" command; usually the timer start after a falling of sda while scl is high (start condition event). if timeout occurs without a valid clock impuls e the status came back to wait_start and the timer will be reinitialized (freeze) in this case the start condition is not validated. function name input parameter return value spi_interrupt_routine void void description isr executed each spi end of transmission. if the received byte is the first byte after the star t condition, the slave check if it is addressed (the slave_address is defined in the i2c.h). if it is addressed, acknowledge will be sent, in the same time the flags slave_read or slave_write will be set according the 8th bit (r/w bit). otherwise, if slave is reading (slave_read is true) the data is stored in i2c_datas_r and acknowledge will be sent; if slave is writing (slave_write is true) set sl ave_wait_msack flag. spi is disabled and the micro is waiting for the next clock to validate the master acknowledge.
function description AN2038 18/23 6.2 protosup module this module contains the high level routine to dispatch the commands frame. function name input parameter return value int_sda_i2c void void description isr generated on each edge of sda. it is used to detect start or stop condition. if a falling edge of sda occurs when scl is high a start condition (to be validated) occurs. in this case the i2c_first_byte will be set to indicate that the next byte s ent is the first byte after start condition, the state is changed in start_ validation and the timer is started calling "start_timer" function. if a rising edge of sda occurs when scl is high a stop condition occurs. in this case the state is changed in wait_start and the "i2c_stop_detected" function is called. function name input parameter return value int_sck_i2c void void description isr generated on each falling edge of the clock. it is used for three purpose: ? if status is starting_validation it will be validated and the status is set to communication. ? if the slave is acknowledging (i2c_slave_ack true) it stop the slave acknowledge. ? if the slave is in waiting of master acknowledge here it is checked and the next byte in i2c_datas_w will be sent. function name input parameter return value test_check_sum void true or false description this function returns true is the checksum received in the read buffer is coherent with the data received, otherwise return false. function name input parameter return value return_crc pointer to data buffer crc calculated description this function returns the crc of the data present in the buffer. the c rc is the sum of the byte in the buffer.
AN2038 function description 19/23 function name input parameter return value new_cde_detected void void description this function writes in the command global variab le the value of the command sent by the master (d1) function name input parameter return value not_ready_function void void description this function writes the output buffer with a frame: stx, 1, not_ready, etx, crc1, crc2 function name input parameter return value not_ack_function void void description this function writes the output buffer with a frame: stx, 1, not_ack, etx, crc1, crc2 function name input parameter return value ack_function void void description this function writes the output buffer with a frame: stx, 1, ack, etx, crc1, crc2 function name input parameter return value master_querry void true or false description this function returns true if the received command frame is a query of the master (request of information to the slave, for example the current speed) other wise it returns false. function name input parameter return value querries_of_master void void description this function fills the data_out buff er according to the master's request.
function description AN2038 20/23 function name input parameter return value test_stx_presence void true or false description this function returns true if stx byte is present in the read buffer, otherwise it returns false. function name input parameter return value fill_data_in void void description this function fills the data_in buffer with the byte present in the read buffer i2c_datas_r and test the etx presence. function name input parameter return value fill_data_valid void void description this function extracts the d1, d2, dn byte from data_in buffer and put them into valid_data_in buffer. function name input parameter return value link_protocol void void description this function performs the dispatching of the commands. this function should be called inside the main loop of the application. if new data is received it tests the presence of stx calling "test_etx_presen ce", if stx is present the checksum is tested calling "test_check_sum()", if the checksum is correct the following calling will be performed: "ack_function" is called "fill_data_valid" is called "new_cde_detected" is called and if "master_querry" calls return true: "querries_of_master" is called.
AN2038 reference and related materials 21/23 7 reference and related materials in the following an it is possible to find info rmation about standard motor control libraries: an1904: stmc ac three-phase induction motor control library an1905: stmc brushless permanent magnet dc motor control library an1947: stmc brushless permanent magnet ac sinus motor control library it is possible to find additional information in the following website: microcontroller at st: mcu.st.com/mcu/ st7mc product information: mcu.st.com/mcu/ > downloads forum: mcu.st.com/mcu/ > forum datasheet: see st7mc datasheet information about softec st7mc starter kit board: see www.softecmicro.com web site
revision history AN2038 22/23 8 revision history table 5. document revision history date revision changes 13-june-2006 1 initial release.
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