Details

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BUY MM74C922 https://www.utsource.net/itm/p/12543496.html

Parameter	Description	Min	Typ	Max	Unit
Operating Voltage (VCC)	Supply voltage range	4.5	-	5.5	V
Quiescent Current (ICC)	Current consumption when idle	-	100	-	μA
Input Leakage Current (IIL)	Maximum current flowing into or out of input pins	-	1	-	μA
Output Sink Current (IOH)	Maximum current that can be sunk by output pin	-	8	-	mA
Output Source Current (IOL)	Maximum current that can be sourced by output pin	-	400	-	μA
Input Voltage (VIH)	High-level input voltage	2.0	-	5.5	V
Input Voltage (VIL)	Low-level input voltage	0	-	0.8	V
Operating Temperature Range	Temperature range for operation	-40	-	85	°C
Storage Temperature Range	Temperature range for storage	-65	-	150	°C

Instructions for Using MM74C922

1. Power Supply:

   • Connect VCC to a stable 5V power supply.
   • Ground all GND pins to ensure proper operation.

2. Input Configuration:

   • Connect the 16-key matrix to the input pins (K1-K4 and R1-R4).
   • Use pull-up resistors (typically 10kΩ) on the row lines (R1-R4) to ensure proper high-level input voltage.

3. Output Configuration:

   • The encoder outputs a 4-bit binary code (Q0-Q3) corresponding to the key pressed.
   • Connect these outputs to your microcontroller or other logic circuits as needed.
   • The encoder also provides an active-low strobe output (STB) which goes low when a key is pressed.

4. Debouncing:

   • The MM74C922 includes internal debouncing circuitry, but additional external debouncing may be necessary for noisy environments.

5. Key Detection:

   • Monitor the STB line to detect when a key is pressed.
   • When STB goes low, read the Q0-Q3 outputs to determine the key pressed.

6. Reset:

   • To reset the encoder and clear the key detection, pull the RESET pin high.

7. Interfacing with Microcontrollers:

   • Use the STB signal to trigger an interrupt in your microcontroller.
   • Read the Q0-Q3 outputs in the interrupt service routine to identify the key.

8. Handling Multiple Key Presses:

   • The encoder can handle multiple key presses, but it will only provide the code for one key at a time. Ensure your system can manage this behavior.

9. Testing:

   • Test the encoder by pressing each key and verifying the correct binary code is output on Q0-Q3.
   • Check the STB signal to ensure it goes low when a key is pressed and returns high when released.

By following these instructions, you can effectively integrate the MM74C922 into your project for reliable key matrix scanning.

(For reference only)