Kathy Quinlan wrote:
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mov a,#10h ;loads accumulator with value 10 hex
mov r1,a ;this and next three lines add a to itself and stores result in r1

Kat,
You are still off base. Your comments describe WHAT happens, not WHY. Both "C" and assembler are "self documenting" as to which values change and by how much, but not as to why you did it.

This describes WHY you coded so

; get the data from next mars rock
; data block (offset 10 from previous)
; R1 point to current data block
mov a,#ROCK_DATA_FIELD_SIZE
add a,r1
mov r1,a ;r1 now point to next block
call get_rock_data ; get the data

By the way, did you know that the mars lander was controlled by a '51 ?

Erik

as to the "what the code does" the above can be made clearer by changing the first 2 lines to:
mov a,r1
add a,#ROCK_DATA_FIELD_SIZE