Interface a typical 12-bit DAC with 8255 and write a program to generate a square waveform of period 12 ms. The CPU runs at 3 MHz clock frequency.

To interface a typical 12-bit DAC (Digital-to-Analog Converter) with the 8255 programmable peripheral interface and Generating Square Wave with 12-Bit DAC and 8255, you need to follow several steps. The 8255 is a general-purpose I/O port chip, and you’ll use it to send data to the DAC to produce the desired waveform. Below is a step-by-step guide for Generating Square Wave with 12-Bit DAC and a simple program in assembly language for an Intel 8085 microprocessor, assuming you are using a CPU with a 3 MHz clock frequency.

Interfacing 12-bit Digital-to-Analog Converter (DAC) with 8255:

1. Connect the DAC to Port A of 8255:
   • Connect the 8 data lines (D0-D7) of the DAC to Port A of the 8255.
   • Connect the DAC’s CS (Chip Select), WR (Write), and other control lines appropriately.
2. Configure 8255:
   • Set the mode of Port A to output mode.
3. Write Program for Generating Square Wave:
   • Write an assembly program to send the appropriate values to the DAC in a loop to generate a square wave.

Assembly Program:

ORG 0000H  ; Set the origin address
; Initialize 8255
MOV C, 82H  ; Control word for 8255 (Port A as output)
OUT 0F0H    ; Send control word to 8255
; Initialize variables
MOV B, 00H  ; Counter for square wave period
LOOP:
  ; Send high value to DAC (replace 3FFH with the desired 12-bit value)
  MOV A, 03FH  ; Data for DAC
  OUT 01H  ; Send data to Port A (connected to DAC)
  CALL DELAY  ; Delay function (half the square wave period)
  ; Send low value to DAC (replace 000H with the desired 12-bit value)
  MOV A, 000H  ; Data for DAC
  OUT 01H  ; Send data to Port A (connected to DAC)
  CALL DELAY  ; Delay function (half the square wave period)
  ; Increment counter and check for the desired period (adjust 30H for desired count)
  INX B
  CPI 30H  ; Check if the counter reached the desired count
  JZ RESET  ; If yes, reset the counter
  JMP LOOP  ; Repeat the loop
DELAY:
  ; Delay function (adjust the count for the desired delay)
  MOV B, 0FFH  ; Outer loop count
DELAY_LOOP:
  MOV C, 0FFH  ; Inner loop count
DELAY_INNER:
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  NOP  ; No operation
  DCR C  ; Decrement inner loop count
  JNZ DELAY_INNER  ; Repeat inner loop if not zero
  DCR B  ; Decrement outer loop count
  JNZ DELAY_LOOP  ; Repeat outer loop if not zero
  RET  ; Return from delay function
RESET:
  ; Reset counter
  MOV B, 00H
  JMP LOOP  ; Jump to the beginning of the loop

Explanation:

1. Initialization:
   • The program starts by setting the 8255 control word, configuring Port A as an output port.
2. Main Program Loop:
   • The main loop continuously sends data to the DAC to generate a high voltage level (full-scale output).
   • It then introduces a delay, followed by sending 0 to the DAC to generate a low voltage level.
   • Another delay follows. This process repeats, creating a square waveform.
3. Delay Function:
   • The delay function is a simple nested loop that provides a delay. You may need to adjust the count for the delay based on the clock frequency of your CPU.
4. Note:
   • This example assumes a 12-bit DAC. Adjust the data values and delay counts based on the specifications of your DAC and the desired waveform characteristics.