SECTION I-3: The ADDLW instruction in the PIC micro-controller

The ADDLW instruction has the following format:

The ADD instruction tells the CPU to add the literal value K to register WREG and put the result back in the WREG register. Notice that in ADDLW, first comes the letter L (literal) and then the letter W (WREG), which means "add a literal value to WREG", the destination. To add two numbers such as 25H and 34H, one can do the following.

PIC WREG and ALU Using Literal Value

Execute the above lines results in WREG = 59H (25H + 34H = 59H)

The following program will add 12H, 16H, 11H, and 43H:

When programming the WREG register of the PIC micro-controller with a literal value, the following points should be noted:

1. Values can be loaded directly into the WREG register. There is no need for a preceding pound sign or dollar sign to indicate that a value is an immediate value as is the case with some other micro-controllers.
2. If values 0 to F are moved into an 8 bit register such as WREG, the rest of the bits are assumed to be all zeros. For example, in "MOVLW 5H" the result will be WREG = 05H; i.e. WREG = 00000101 in binary.
3. Moving a value larger than 255 (FF in hex) into the WREG register will truncate the upper byte and cause a warning in the .err file.