Free Electronic Circuits & 8085 projects

Electronic projects with circuit diagram and 8085 microprocessor projects.

8 x 8 Keyboard Interface(Without Interrupt signal)

Statement: Interface an 8 x 8 matrix keyboard to 8085 through 8279 in 2-key lockout mode and write an assembly language program to read keycode of the pressed key. The external clock frequency is 2MHz. Use I/O mapped I/O technique. (Dont use any Interrupts)

HARDWARE FOR 8 x 8 MATRIX KEYBOARD INTERFACE

73.a-8 x 8 Keyboard Interface(Without Interrupt signal)

73.b-8 x 8 Keyboard Interface(Without Interrupt signal)

SOFTWARE FOR 8 x 8 MATRIX KEYBOARD INTERFACE

The three steps needed to write the software are:

Step 1: Find keyboard/display command word.

73.c-8 x 8 Keyboard Interface(Without Interrupt signal)

 

 

 Step 2: Find program clock command word

73.d-8 x 8 Keyboard Interface(Without Interrupt signal)

Step 3: Find Read FIFO/sensor RAM command word.

73.e-8 x 8 Keyboard Interface(Without Interrupt signal) 

Source program:

  • MVI A, 00H : Initialize keyboard/display
  • OUT 81H : in encoded scan keyboard-2 keylockout mode
  • MVI A, 34H
  • OUT 81H : Initialize prescaler count
  • BACK: IN 81H : Read FIFO status word
  • ANI 07H : Mask bit B3 to B7
  • JZ BACK : If 0, key is not pressed wait for key press else read FIFO RAM
  • MVI A, 40H : Initialize 8279 in read
  • OUT 81H : FI FO RAM mode
  • IN 80H : Read FIFO RAM (keycode)
  • HLT : Stop program execution.

Flowchart

73.f-8 x 8 Keyboard Interface(Without Interrupt signal) 

Related Programs (Click down)

Flashing of LEDs

Traffic Light Control

Stepper Motor Control

Keyboard interface(64-key-matrix-keyboard)