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:
- 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.
- Configure 8255:
- Set the mode of Port A to output mode.
- 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:
- Initialization:
- The program starts by setting the 8255 control word, configuring Port A as an output port.
- 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.
- 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.
- 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.