IBM 5150 - 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