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CPDR

Block compare with decrement.
Function: A - [HL]; HL <- HL - 1; BC <- BC - 1
Repeat until BC = 0 or A = [HL]
 
Format:
1110 1101
 
byte 1: ED
 
1011 1001
 
byte 2: B9
 
Description: The contents of the memory location addressed by the HL register pair are subtracted from the contents of the accumulator and the result is discarded. Then both the BC register pair and the HL register pair are decremented. If BC != 0 and A != [HL], the program counter is decremented by two and the instruction is re-executed.
 
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Example:

OBJECT CODE
Before:
 
After: