turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104 part number 74c922 - so december 2012 page 1 of 5 74c922 - so ic keyboard / keypad encoder for up to 16 switches mm74c922 replacement ic general description the 74c922 - so is designed as a replacement chip for the obsolete mm74c922 surface mount part. the 74c922 - so contains all the logic necessary to enc ode a spst keyboard switch array up to 4 by 4 in size and provide a 4 bit parallel output and a data available signal. the data available signal goes high when a key is pressed, and goes low before another key output is generated. the data output pins ke ep their state even after the key is released. the array can be a 4 x 4 array, but smaller arrays such as a 3 x 4 array or any smaller size can be used. the 74c922 - so handles debouncing of the keys as well. no external cap acitors are required for timing ; all timing is internally generated. no external diodes are required in the array to prevent key ghosting in a two key rollover situation. a .1 uf bypass capacitor is sug gested across the vdd and vss pins. the part uses the standard 20 pin .3 inch wid th soic package. features replacement chip for mm74c922 fully encodes a key switch array . (up to 4 x 4) no external parts required . low power consumption 1.5 ma typical. supply voltage 2.4 to 5 .25 volts . last key pressed retained on data outputs . all tim ing internally generated . 2 key rollover . on chip row input resistors . internal key bounce elimination . ttl and cmos compatible outputs . part is in full production . soic 20 pin package . rohs compliant low emi
turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104 part number 74c922 - so december 2012 page 2 of 5 example circuit data out c 74C922-SO 11 5 12 13 14 15 1 2 3 4 6 7 9 10 18 8 16 19 20 17 colx2 nc colx1 dataavail nc nc rowy1 rowy2 rowy3 rowy4 nc nc colx3 vss dataoutb colx4 dataoutd dataouta vdd dataoutc 2.4 - 5 v data available data out d data out a keyboard data out b connection diagram 74C922-SO 11 5 12 13 14 15 1 2 3 4 6 7 9 10 18 8 16 19 20 17 colx2 nc colx1 dataavail nc nc rowy1 rowy2 rowy3 rowy4 nc nc colx3 vss dataoutb colx4 dataoutd dataouta vdd dataoutc p in description pin # description pin # description 1 row y1 20 vdd 2 row y2 1 9 data out a 3 row y3 1 8 data out b 4 row y4 1 7 data out c 5 nc 1 6 data out d 6 nc 1 5 nc 7 nc 1 4 nc 8 col x4 1 3 data avail 9 col x3 1 2 col x1 10 vss 2 1 col x2 col x1 ? col x4 these pins are open drain column driver outputs to the key matrix . row y1 ? row y4 these pins are the row inputs from the key matrix . these inputs have 5.6k (nominal) pull up resistor s on chip.
turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104 part number 74c922 - so december 2012 page 3 of 5 data out a ? data out d these pins are the encoded data output. the output keeps th e state of the last key pressed even after the key is released. these pins are ttl and cmos compatible. data avail this pin goes high when a key is pressed, and low when a key is released. this pin goes low in a two key rollover situation before returning high. this pin is ttl and cmos compatible. vss connect to system ground. vdd connect to supply voltage of 2.4 to 5 volts . a .1 uf decoupling capacitor to ground is recommended. notes: no connection is required to the nc pins . if external capacitors are used on pins 6 and 7 from your previous design, they do not need to be removed. if pin 14 is grounded on your previous design, it does not need to be changed. pin s 5 and 15 must be left unconnected . truth table colx1 colx2 colx3 colx4 dataoutd dataoutc dataoutb dataouta rowy1 x 0 0 0 0 rowy1 x 0 0 0 1 rowy1 x 0 0 1 0 rowy1 x 0 0 1 1 rowy2 x 0 1 0 0 rowy2 x 0 1 0 1 rowy2 x 0 1 1 0 rowy2 x 0 1 1 1 rowy3 x 1 0 0 0 rowy3 x 1 0 0 1 rowy3 x 1 0 1 0 rowy3 x 1 0 1 1 rowy4 x 1 1 0 0 rowy4 x 1 1 0 1 rowy4 x 1 1 1 0 rowy4 x 1 1 1 1 absolute maximum ratings symbol description min typical max units notes t stg storage t emperature - 55 25 + 100 oc t a oper ating temperature - 40 +85 oc v dd v dd - v ss voltage - 0 .5 +6.0 v v io input voltage v ss - 0 .5 v dd + 0 .5 v i mio maximum current into any pin - 25 +50 ma esd electrostatic discharge voltage 2000 v human body model esd lu latch up current 200 ma
turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104 part number 74c922 - so december 2012 page 4 of 5 dc electrical characteristics symbol description min typical max units notes v dd s upply voltage 2.4 5.25 v i dd supply current 1.5 8 ma v dd = 5v v oh high output level v dd - 1.0 v i oh =10 ma v ol low output voltage 0.75 v i ol =25 ma v ih inpu t high level 2.1 v v il input low level 0.8 v i oh high level source current 10 ma i ol low level sink current 25 ma c io capacitive load 3.5 10 pf i il input leakage 1 na r pu pull up resistors on row inputs 4 5.6 8 k ? differences between the mm74c922 and 74c922 - so power supply the mm74c922 part is capable of a supply voltage of 3 to 1 5 volts. the 74c922 - so has a more limited power supply of 2.4 to 5.25 volts. timing capacitors the mm74c922 part requires timing capacitors on pins 6 and 7. the 74c922 - so generates all timing internally, and these capacitors are not required. these pins are no connects on the 74c922 - so. if capacitors are present on your design, they do not need to be removed. tristate outputs th e dataout pins of the mm74c922 are tristate outputs controlled by pin 14 ? outputenable. the dataout pins of the 74c922 - so are not tristate. pin 14 is a no connect, and may be grounded or left open. if your design needs tristate outputs, consult the fact ory for solutions. timing the timing of the 74c922 - so is more relaxed. the data setup to data avail timing is longer, and the low output time in a two key ro ll over situation is improved . theory of operation the 74c922 - so is a custom programmed micro processor designed to emulate the mm74c922. the open drain colx pins are pulsed low one at a time, and the rowy pins are sampled to check for key switch closures. if a key is detected, scanning stops until the key is released. the pressed key is encoded and placed on the dataout pins, and the dataavail output is set low until the key is released. when the key is released, the dataavail output is set hi gh again and scanning continues.
turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104 part number 74c922 - so december 2012 page 5 of 5 physical dimensions mm74c922.com is a part of: turning ideas into reality abcircuits www.abcircuits.com pob 123 new hill nc 27562 (919) 290 - 7104
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