Intel 8080 - B4_Page_24

Chapter 6. Programming Techniques
6-4
For example, the subroutine ADSUB expects the address of a three-byte parameter list in the Hand L registers.
It adds the first and second bytes of the list, and stores the result in the third byte of the list:
Label Code
LXI
CALL
RET1 :
PLlST:
DB
DB
DS
LXI
CALL
RET2:
L1ST2:
DB
DB
DS
ADSUB:
MOY
INX
MOY
ADD
INX
MOY
RET
Operand
H,PLlST
ADSUB
6
8
H,L1ST2
ADSUB
10
3S
A,M
H
B,M
B
H
M,A
Comment
;LOAD HAND L WITH
;ADDRESSES OF THE PARAM-
;ETER LIST
;CALL THE SUBROUTINE
;FIRST
NUMBER TO BE ADDED
;SECOND NUMBER TO BE
;ADDED
;RESULT
WILL BE STORED HERE
;LOAD HAND L REGISTERS
;FOR ANOTHER
CALL TO ADSUB
;GET
FIRST PARAMETER
;INCREMENT MEMORY
;ADDRESS
;GET
SECOND PARAMETER
;ADD
FIRST TO SECOND
;INCREMENT MEMORY
;ADDRESS
;STORE RESULT AT THIRD
;PARAMETER STORE
;RETURN UNCONDITIONALLY
The first time ADSUB is called, it loads the A and B registers from PLiST and PLlST+l respectively, adds them,
and stores the result in PLiST +2. Return is then made to the instruction at RETl.