IBM 5150 Hardware Reference Manual page 265

LOC OBJ
LINE SOURCE
F97E EBF9
5268
"20
5269 ENDP
5270 ; ---------­ ---------------------------------­
f9BO 5271
NEAR
5272
PURPOSE:
5273 TO COMPUTE TIME TIll
~EXT
DATA
5274 TRANSITION (EDGE)
5275
5276 ; ON ENTRY:
5Z77 ;
EDGE_CNT CONTAINS LAST EDGE COUNT
5278
5279 ; ON EXIT:
52&0 ; AX CONTAINS OLD LAST EDGE COUNT
5281 I BX CONTAlNS PULSE WIDTH {HALF Bn I
5282 ; -------------­ ---------.--------------. ­
F'eo
696400 5283 MOV
ex.
100
j
SET TIME TO WAn FOR BIT
F983 BA266BOO 5284
MOV
AH.LAST_VAl
JGET PRESENT INPUT VALUE
F987
5285 Nee:
~
Fm-H-BIT
F987 E462 5286 IN
AL.POIH_C
; INPUT DATA
BIT
f989 2410 5237 AND AL,OlOH ;MASK OFF EXTRANEOUS
BITS
F988 3AC4­
5288 CMP AL,AH ;SAME AS BEFORE?
FgeD ElFS 5269 LOOPE
"22
; LOOP TILL
IT
CHANGES
F9SF A26BOO 5290
MOV
LAST_VAL,AL
JUPDATE LAST_VAL WITH NEW VALUE
F992 BOOD 5291 MOV
Al;O jREAD TIMER'S COUNTER eONHA.ND
F9'94 E643 5292
OUT
TIM_CTL,AL
; LATCH COUNTER
F996 E440 5293 HI
AL,
TIMERO ;GET LS
eYTe
F998 8AEO 52'4
I10Y AH,Al ,SAVE IN Aft
fY.,,,, 1:'"0
SUS
IN
Al, TIMERO ,GET
HS
BYTE
F99C 8bC" 5296 XCHG Al,AH ,XCHG Al,AH
F99E 8Bl£6700
5n7
MOV
BX,EDGE_CNT
; BX GETS LAST EDGE
COUNT
F942 2B08
5298 SUB BX,AX ; SET BX EQUAL TO HALF BIT PERIOD
F9"4 1\36700
5299 MOV EDGE_CNT ,AX
; UPDATE EDGE CO""'T;
F9A7 Cl 5300
RET
5301 !fEAD_HALF
_BIT
ENDP
5302
;--------------------_
...
_--_ . .
_------------­
F9A8
5303
PROC
NEAR
5304
5305 ; WRITE 1 OR MORE 256 BYTE BLOCKS TO CASSETTE.
5306 THE OATA IS PADDED TO FILL OUT THE LAST 256 BYTE BLOCK.
5307
530S ; ON ENTRY:
5309 BX POINTS TO MEMORY BUFFER ADDRESS
5310
ex
CONTAINS HUMBER OF BYTES TO WRITE
5311
;:512 ; ott
EXIT:
5313 BX POINTS
1
BYTE PAST LAST BYTE WRITT-EN TO CASSETTE
5314 ex IS ZERO
5315
;-------------------------------------------­
F9AS 53
5316 PUSH
ax
F9.9 51 5317
PUSIt
cx
F9,u, E461
5318 IN AL,PORT_B
;DISABLE SPEAKER
f9AC 24FO 53n
AND
AL,NOT 02H
F9AE DeOI 5320 OR AL. 01H ENABLE TInER
F980 E661 5321 OUT PORT_B.AL
F962 BOB6 5322 MOV AL,OB6H SET UP TIMER .. - MODE 3 SQUARE WAVE
F964 E643
$3,3
OUT
TIM_CTLtAl
F9B6 E8A600 5324
CALL BEGIN.OP
; START MOTOR AND DELAY
F9B9 BeA004
5325
NOV
AX,llS4
; SET NORMAL BIT SIZE
F98C E88500
5326 CALL ""
J
SET_TIMER
F9BF MOOOS 5327 MOV CX.0800H
;SH CX FOR lEADER BYTE COUNT
F9C2 5328 W23:
; WRITE LEADER
F9C2 F9 53,9
STC ; WR
ITE ONE BITS
F9Cl E86800 5330 CALL Wl?ITE_BIT
F9C6 EZFA 5331 LOOP "e> ; LOOP • TIL LEADER IS WRITTEN
F9C8 F8
5332
CLC
;tRITE SYNC BIT
to J
F9C9 £86200
5333 CALL WRITE...8IT
F9CC S9
5334
pop
ex
;RESTORE REGS CX,BX
FqCD 58 5335 POP
BX
F9CE B016
5336 MoV AL. 16M
I WRITE SYH CHARACTER
F900 E84400 5337 CALL WRITE_BYTE
A-72