Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 KBDSER56 IC Serial output encoder keyboards up to 56 switches General Description The KBDSER56 IC is designed to provide a serial ASCII output encoder for keyboards up to 56 keys. The KBDSER56 IC contains all the logic necessary to encode a SPST keyboard switch array up to 7 by 8 in size and provide a serial ASCII output. The output is standard asynchronous format, using 8 bits, 1 stop and no parity at 9600 BPS. Other formats and encoding are available, contact the factory. The array can be a 7 x 8 array, but any smaller size may be used. The KBDSER56 IC handles debouncing and encodes the keys with no external parts. 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 suggested across the VDD and VSS pins. The part uses the standard 20 pin .3 inch width SOIC package. Features • Asynchronous serial output • Fully encodes a key switch array. • • • • • • • • • • • • (up to 7 x 8) No external parts required. Low power consumption 5 mA typical. Supply voltage 2.4 to 5.25 volts. All timing internally generated. 2 Key rollover. On chip row input resistors. Applications • Data Entry • Security Alarms • Handheld devices • Machine Control • Numeric Entry • Telephones • Computers • Controls • Gaming Internal key bounce elimination. TTL and CMOS compatible outputs. Part is in full production. SOIC and DIP 20 Pin Package. ROHS Compliant Low EMI Part Number 74C922-SO Copyright © 2014 ABCircuits. Revised September 2014 Page 1 of 7 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 Example Circuits 56 KEY RS232 KEYBOARD KBDSER56 1 2 3 4 5 6 7 8 9 10 ROWY8 ROWY6 ROWY4 ROWY2 NC SOUT COLX6 COLX4 COLX2 VSS VDD ROWY7 ROWY5 ROWY3 ROWY1 NC COLX7 COLX5 COLX3 COLX1 C5 .1 VCC 20 19 18 17 16 15 14 13 12 11 1 C1+ 3 C6 .1 C2+ 10 12 R7 R8 28 29 2A 2B 2C 2D 2E 2F C3 30 31 32 33 34 35 36 37 C4 38 39 3A 3B 3C 3D 3E 3F C6 C7 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 57 55 56 T1out T2in T2out GND R5 C2 +5 C7 .1 2 6 C8 .1 R1in R2in RS232 DB9S J1 1 2 3 4 5 6 7 8 9 8 14 7 13 8 TXD GND 15 R4 27 C5 40 41 R6 R3 R2 R1 25 26 T1in R2out KEYPAD 24 V- R1out 9 23 V+ C2- 11 21 22 U2 SEE NOTES C1- 4 5 C1 20 VCC 16 VCC U2= MAX232 FOR 5V RS232 U2= MAX3232 FOR 3V RS232 56 KEY RS-485 KEYBOARD VCC KBDSER56 1 2 3 4 5 6 7 8 9 10 ROWY8 ROWY6 ROWY4 ROWY2 NC SOUT COLX6 COLX4 COLX2 VSS VDD ROWY7 ROWY5 ROWY3 ROWY1 NC COLX7 COLX5 COLX3 COLX1 VCC U2 20 19 18 17 16 15 14 13 12 11 1 VCC 2 3 4 21 22 23 24 25 26 29 2A 2B 2C 2D 2E 2F 31 32 33 34 35 36 DO / RI DI GND 7 6 RS485 OUT 5 37 38 39 3A 3B 3C 3D 3E 3F 40 41 42 C 6 48 49 4A 4B 4C 4D 4E 4F 51 52 C7 DE 8 27 C 3 30 C5 -DO/-RI R8 R7 R6 R5 R4 R3 R2 R1 20 C 2 28 C4 VCC -RE U2 75176 FOR 5V U2 MAX3485 FOR 3.3V KEYPAD C1 RO 50 43 53 44 54 45 55 46 56 47 57 Part Number KBDSER56 Copyright © 2014 ABCircuits. Revised September 2014 Page 2 of 7 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 56 KEY ETHERNET KEYBOARD +3.3 ROWY8 ROWY6 ROWY4 ROWY2 NC SOUT COLX6 COLX4 COLX2 VSS +3.3 VDD ROWY7 ROWY5 ROWY3 ROWY1 NC COLX7 COLX5 COLX3 COLX1 20 19 18 17 16 15 14 13 12 11 LANTRONIX XPORT 1 2 3 4 5 6 7 8 GND +3.3 -POR OUT IN CP1 CP2 CP3 R4 R5 R6 R7 R8 21 22 23 24 25 26 27 C2 28 29 2A 2B 2C 2D 2E 2F C3 30 31 32 33 34 35 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 C4 C5 C6 C7 R3 20 C1 R2 R1 KEYPAD 36 46 56 37 47 57 Connection Diagram KBDSER56 1 2 3 4 5 6 7 8 9 10 ROWY8 ROWY6 ROWY4 ROWY2 NC SOUT COLX6 COLX4 COLX2 VSS VDD ROWY7 ROWY5 ROWY3 ROWY1 NC COLX7 COLX5 COLX3 COLX1 20 19 18 17 16 15 14 13 12 11 Pin Description Pin # 1 2 3 4 5 6 7 8 9 10 Description Row Y8 Row Y6 Row Y4 Row Y2 NC SOUT Col X6 Col X4 Col X2 VSS Pin # 20 19 18 17 16 15 14 13 12 21 Description VDD Row Y7 Row Y5 Row Y3 Row Y1 NC Col X7 Col X5 Col X3 Col X1 Part Number KBDSER56 Copyright © 2014 ABCircuits. Revised September 2014 Page 3 of 7 ETHERNET KBDSER56 1 2 3 4 5 6 7 8 9 10 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 Col X1 – Col X7 These pins are open drain column driver outputs to the key matrix. Row Y1 – Row Y8 These pins are the row inputs from the key matrix. These inputs have 5.6K (nominal) pull up resistors on chip. SOUT This is the serial output pin. It may be tied directly to the UART receiver input of your UART or microprocessor; to a RS -232 driver such as the MAX232; a standard RS485 driver such as the 75176 or an Ethernet interface such as the Lantronix Xport. This pin is high in the idle state, the output format is 8 bits, 1 stop, no parity at 9600 BPS. Other output formats and baud rates are available, please contact the factory for information. 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: Make no connection to the NC pins. Pins 5 and 15 must be left unconnected. Truth Table The ASCII output codes of the KBDSER56 were chosen to make it easier to design, diagnose and translate codes easier. The ASCII outputs can be seen using any terminal program such as Hyperterm, and easily translated by subtracting 32 (020h), and then using the remainder as an offset into a translation table. Custom output codes are available, consult the factory for information. COLX1 COLX1 COLX1 COLX1 COLX1 COLX1 COLX1 COLX1 COLX2 COLX2 COLX2 COLX2 COLX2 COLX2 COLX2 COLX2 COLX3 COLX3 COLX3 COLX3 COLX3 COLX3 COLX3 COLX3 ROWY1 X ROWY2 ROWY3 ROWY4 ROWY5 ROWY6 ROWY7 ROWY8 X X X X X X X X X X X X X X X X X X X X X X X ASCII OUT SPACE ! “ # $ % & ‘ ( ) * + , . / 0 1 2 3 4 5 6 7 Part Number KBDSER56 Copyright © 2014 ABCircuits. Revised September 2014 Page 4 of 7 HEX 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 COLX4 COLX4 COLX4 COLX4 COLX4 COLX4 COLX4 COLX4 COLX5 COLX5 COLX5 COLX5 COLX5 COLX5 COLX5 COLX5 COLX6 COLX6 COLX6 COLX6 COLX6 COLX6 COLX6 COLX6 COLX7 COLX7 COLX7 COLX7 COLX7 COLX7 COLX7 COLX7 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O P Q R S T U V W 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 Absolute Maximum Ratings Symbol Description Tstg Ta V dd V io Imio ESD Storage Temperature Operating Temperature LU Latch up current V dd - V ss Voltage Input Voltage Maximum current into any pin Electrostatic Discharge Voltage Min -55 -40 -0.5 Vss - 0.5 -25 2000 Typical Max Units 25 +100 +85 +6.0 ºC ºC V V mA V V dd +0.5 +50 200 Notes Human Body Model ESD mA Part Number KBDSER56 Copyright © 2014 ABCircuits. Revised September 2014 Page 5 of 7 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 DC Electrical Characteristics Symbol Description V dd Idd V oh V ol V ih V il Ioh Iol Cio Iil Rpu Supply Voltage Supply Current High Output Level Low Output Voltage Input High Level Input Low Level High Level Source Current Low Level Sink Current Capacitive load Input leakage Pull Up Resistors On Row Inputs Min Typical Max Units 5 5.25 8 V mA V V V V mA mA pF nA k? 2.4 V dd - 1.0 0.75 2.1 4 3.5 1 5.6 0.8 10 25 10 8 Notes Note 1 Ioh=10 mA Iol=25 mA Note 1: Vdd=5VDC, all inputs and outputs open Theory Of Operation The KBDSER56 IC is a custom programmed microprocessor designed to encode keyboards and provide a serial output. 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 to ASCII and transmitted in standard asynchronous format on the SOUT key. The key is transmitted using 8 data bits, 1 stop bit and no parity. Baud rate is 9600 BPS. When the key is released scanning continues. Part Number KBDSER56 Copyright © 2014 ABCircuits. Revised September 2014 Page 6 of 7 Turning Ideas Into Reality ABCircuits www.abcircuits.com POB 123 New Hill NC 27562 (919) 290-7104 Physical Dimensions – 20 Pin DIP (-DIP Suffix) Physical Dimensions – 20 Pin SOIC Close but not quite? Our products are software based, we can modify existing parts to fit your needs at a minimal cost or create new parts designed to your specifications. Email us and we can make a chip for you! For the latest version of this spec sheet, visit www.abcircuits.com Design Services Available We can quickly turn your idea into a chip, a pc board, or a finished product. Contact us with your needs and specifications. Part Number KBDSER56 Copyright © 2014 ABCircuits. 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