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PHYSICAL DESIGN AND DEBUGGING
PAGE
66,132
EQUATES
,
LATCH
EQU
0C8H
;PRESUMES
A
HARDWARE
;LATCH
IS
AT
I/O
ADDR
C8H
GOOD-SIGNAL
EQU
0AAH
BAD-SIGNAL
EQU
055H
CODE
TO
VERIFY
ABILITY
TO
WRITE
AND
READ
RAM
CORRECTLY
ASSUME
CS:INITIAL_CODE
INITIAL_CODE
SEGMENT
ORG
0F000H
;THIS
IS
INTENDED
TO
BE
LOCATED
;AT
PHYSICAL
ADDRESS
FFFFF000H
TSLLOOP:
MOV
BX,
0000H
;INITIALIZE
BASE
~EGISTER
TO
0
MOV
DS,
BX
;INITIALIZE
DS
REGISTER
TO
0
MOV
rBX],
5473H
;WRITE
5473H
TO
RAM
ADDR
0
AND
1
MOV
rBX]+2,
2961H
lWRITE
2961H
TO
RAM
ADDR
2
AND
3
JMP
READ
lJMP
TO
FORCE
CPU
TO
BREAK
lPRE-FETCH
QUEUE
AND
FETCH
THE
lNEXT
INSTRUCTION
AGAIN.
THIS
lPREVENTS
THE
RAM
DATA
WRITTEN
lFROM
JUST
LINGERING
ON
THE
DATA
lBUS
UNTIL
THE
READ
OCCURS
READ:
CMP
rBX],
5473H
lREAD
DATA
FROM
RAM
AD
DR
0
AND
1
;AND
COMPARE
WITH
VALUE
WRITTEN
JNE
BADRAM
;IF
DATA
DOESN'T
MATCH,
THEN
JMP
CMP
rBX]+2,
2961H
lREAD
DATA
FROM
RAM
ADDR
2
AND
3
lAND
COMPARE
WITH
VALUE
WRITTEN
JNE
BADRAM
;IF
DATA
DOESN'T
MATCH,
THEN
JMP
MOV
.AL,
GOOD-SIGNAL
OUT
LATCH,
AL
lSIGNAL
THAT
DATA
WAS
CORRECT
JMP
TSLLOOP
BADRAM:
MOV
AL,
BAD-SIGNAL
OUT
LATCH,
AL
lSIGNAL
THAT
DATA
WAS
BAD
JMP
TSLLOOP
ORG
0FFF0H
lPOSITION
THE
FOLLOWING
INSTRUCTION
lAT
OFFSET
0FFF0H
START:
JMP
TST-LOOP
lINTRA-SEGMENT
JUMP
(WITHIN
l
SEGMENT)
lTHIS
IS
INTENDED
TO
BE
THE
FIRST
lINSTRUCTION
EXECUTED,
SO
IT
MUST
lBE
LOCATED
AT
PHYSICAL
ADDRESS
lFFFFFFF0H.
INITIAL_CODE
ENDS
END
Figure 11-29. More Complex Diagnostic Program
11-38