MM74C923

Features:

 50 kW maximum switch on resistance
 On or off chip clock
 On-chip row pull-up devices
 2 key roll-over
 Keybounce elimination with single capacitor
 Last key register at outputs
 3-STATE output LPTTL compatible
 Wide supply range: 3V to 15V
 Low power consumption


Pinout




Specifications

Voltage at Any Pin                            VCC - 0.3V to V CC + 0.3V
Operating Temperature Range
MM74C922, MM74C923                                    -40°C to +85°C
Storage Temperature Range                          -65°C to +150°C
Power Dissipation (P _D)
Dual-In-Line                                                                  700 mW
Small Outline                                                                 500 mW
Operating V_CC Range                                                 3V to 15V
V_CC                                                                                      18V
Lead Temperature
(Soldering, 10 seconds)                                                  260°C


Description

   The MM74C922 and MM74C923 CMOS key encoders provide all the necessary logic to fully encode an array of SPST switches. The keyboard scan can be implemented by either an external clock or external capacitor. These encoders MM74C923 also have on-chip pull-up devices which permit switches with up to 50 kW on resistance to be used. No diodes in the switch array are needed to eliminate ghost switches. The internal debounce circuit needs only a single external capacitor and can be defeated by omitting the capacitor. A Data Available output of MM74C923 goes to a high level when a valid keyboardentry has been made.

   The Data Available output of MM74C923 returns to a low level when the entered key is released, even if another key is depressed. The Data Available will return high to indicate acceptance of the new key after a normal debounce period; this two-key roll-over is provided between any two switches. An internal register of MM74C923 remembers the last key pressed even after the key is released. The 3-STATE outputs provide for easy expansion and bus operation and are LPTTL compatible.