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SECTION V-8: Using EQU for RAM Address Assignment
The common usage of EQU is for the address assignment of the general purpose region of the file register. Examine the following rewrite of an earlier example using EQU:
| MYREG EQU 0x12 | ;assign RAM location to MYREG |
|---|---|
| MOVLW 0 | ;clear WREG, WREG = 0 |
| MOVWF MYREG | ;clear MYREG, location 12H has 0 |
| MOVLW 22H | ;WREG = 22H |
| ADDWF MYREG, F | ;MYREG = WREG + MYREG |
| ADDWF MYREG, F | ;MYREG = WREG + MYREG |
| ADDWF MYREG, F | ;MYREG = WREG + MYREG |
| ADDWF MYREG, F | ;MYREG = WREG + MYREG |
This is specially helpful when the address needs to be changed in order to use a different PIC chip for a given project. It is much easier to refer to a name than a number accessing RAM address locations.
The following program will move value 9 into RAM locations 0 - 4, then add them together and place the sum in location 10H
| MYVAL EQU 9 | ;MYVAL = 9 |
|---|---|
| R0 EQU 0 | ;assign RAM addresses to R0 |
| R1 EQU 1 | ;assign RAM addresses to R1 |
| R2 EQU 2 | ;assign RAM addresses to R2 |
| R3 EQU 3 | ;assign RAM addresses to R3 |
| R4 EQU 4 | ;assign RAM addresses to R4 |
| SUM EQU 10H | |
| MOVLW MYVAL | ;WREG = 9 |
| MOVWF R0 | ;RAM location 0 has 9 |
| MOVWF R1 | ;RAM location 1 has 9 |
| MOVWF R2 | ;RAM location 2 has 9 |
| MOVWF R3 | ;RAM location 3 has 9 |
| MOVWF R4 | ;RAM location 4 has 9 |
| MOVLW 0 | ;WREG = 0 |
| ADDWF R0, W | ;WREG = R0 + WREG |
| ADDWF R1, W | ;WREG = R1 + WREG |
| ADDWF R2, W | ;WREG = R2 + WREG |
| ADDWF R3, W | ;WREG = R3 + WREG |
| ADDWF R4, W | ;WREG = R4 + WREG |
| MOVWF SUM |