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ECED 3204. Microprocessors
M68HC11 Microcontroller
Advantages of Named Constants
1. Their value only needs to be changed once (in the Definition Part)
2. Improves readability of Assembly Code
Other Examples:
; Constants
DELAY
equ
2000
; Delay value to initialize counter with
BITMASK1 equ
%00000001 ; Mask used for parity, bit 0 (B0)
BITMASK2 equ
%00110000 ; Mask used to toggle bits 4 & 5 (B4 & B5)
; Instructions (These are just isolated examples, NOT part of a program)
ldx
#DELAY
; Initializing delay counter IX
bita
#BITMASK1 ; Checking if B0 is 0 or 1, <ACCA> even or odd
anda #BITMASK1 ; Does the same as bita but also modify ACCA
; In this case ACCA B1-B7 are cleared
eora #BITMASK2 ; Toggles ACCA bits 4 & 5 (B4 & B5)
Dalhousie University
62
Jose A. Gonzalez-Cueto