IBM 5150 - Page 266

LOC OBJ
LINE
SOURCE
5338
;--------------------------------------------
5339
I
WRITE 1 OR HORE 256 BYTE BLOCKS TO CASSETTE
5340
5341
I
ON. ENTRY:
5342 ax POINTS TO MEMORY BUFFER ADDRESS
5343 ex CONTAINS NUMBER OF BYTES TO WRITE
5344
~
5345
ON EXIT:
5346
BX POUITS 1 BYTE PAST LAST BYTE WRITTEN TO CASSETTE
5347
ex IS ZERO
5348
; ...... ------------------- .. -- -------------- ----
FOO3
5349 WR_BLOCK:
F9D3 C7066900fFFF 5350
HOV
CRC_REG,OFFFfH IINIT CRe
F909 BAgDOl
5351
MOV
DX,256 ;FOR 2:56 BYTES
F90C 5352
W24: ; W~-BlK
F9DC 268A07 5353
HOV
AL,Es:[ex] ; READ BYTE FROM MEM
F90F E83500
5354
CALL WRITE_BYTE
jWRITE IT TO CASSETTE
F9EZ
£302 5355
JCXZ
"25
jUNLESS CX=O, ADVANCE PTRS & DEC COUNT
F9£4 43
5356
INC OX j INC BUF f ER POINTER
F9E5 49
5357
DEC
CX
50EC BYTE COUNTER
F9E6
5358 WZ5:
f SKIP-ADV
F9E6 4A
535'
DEC
ox ,DEC BLOCK CNT
F9E7 7FFl
5360
JG H2. ; LOOP TILL 256 BYTE BLOCK
5361 ; IS WRITTEN TO TAPE
5362
;------------------- WRITE eRe --------------
5363
I
WRITE l'S COHPLEMENT OF eRe REG TO CA~SETTE
536. ;
WHICH IS CHECKED FOR CORRECTNESS WHEN THE BLOCK IS READ
5365
5360 ; REG AX IS MODIFIED
5367
, ... -----------------------------------------
F9E9 A16900
5365 HOV
AX,CRC_REG ;WRITE THE ONE'S CQtlPLEMENT OF THE:
5369 ;
TWO BYTE CRC TO TAPE
F9EC
F7DO 5370
NOT AX ; FOR l' S COMPLEMENT
F9EE SO
5371
PUSH AX ;SAVE IT
F9EF UEO 5372:
XCH.
AH,Al
;WRITE t15 BYTE FIRST
F9Fl 182300
5373
CALL
WRITE_BYTE
;WRITE IT
~
F9F4 58 5374
POP
AX
,GET IT BACK
F9F5 E81FOO
5375
CALL WRlTE_BYTE
,NOlo! WRITE LS BYTE
F9F6 OBe9
5376
OR CX,CX ;IS BYTE COUNT EXHAUSTED?
F9FA 7507
5377
JHZ WR_BLOCK
;JUHP IF NOT DONE YET
F9FC
51 5378
PUSH
CX
iSAVE REG ex
F9FD 892000 5379
MOV ex, 32
;WRITE OUT TRAILER BITS
FAOO 5380 WZ6:
j TRAIL-LOOP
FAOO F9
5381
STC
FA01 E82AOO
5382 CALL
WRITE_BIT
FA04 E2FA
5383
LOOP HZO I WRITE UNTIL TRAILER WlunEN
FA06 59 5384
POP CX ,RESTORE REG CX
FA07 B080 5385
MOV AL. OBOH ; TURN TIttER2 Off
FA09 £643
5386 OUT
TIt-ccn, AL
FAOB
B80100 5387 HOV
AX. 1
FADE E83300
5388 CALL W31 ; SET_TIMER
FAll E87AFE 5389
CALL MOTOR_OFF I TURN HOTOR OFF
FA14 2BCO
5390
SUB AXJAX
;NO
ERRORS REPORTED ON WRITE OP
FAll. C3
5391 RET ;FINlsHEO
5392
WRITE_BLOCK EHOP
5393
1------------------------------------------
FA17
53"
WRITE_BYTE PRoe NEAR
5395
;
WRITE A BYTE TO CASSETTE.
5396
;
BYTE TO WRITE IS IN REG At.
5397
; ---- ... ---------------_ ... _------------- --------
FA17 51 5398
PUSH CX
;SAVE REGS CX,AX
FA18 50
5399
PUSH AX
FA19 8Af8 5400
MDV CHJAL ;AL=BYTE TO WRITE.
5401 f NS BIT WRIITEN FIRST}
FA1S BI08 5402
NOV CL.8
;FOR e DATA BITS IN BYT!.
~
5403
NOTE: TWO EDGES PER BIT
'AID
5404 W27:
I DISASSEMBLE
THE DATA BIT
FA1D 0005 5405
RCL
eH,1 IROTATE MS BIT lNTO CARRY
FAIF 9C 5406
PUSHF ;SAVE FLAGS.
5407 NOTE: DATA 81T IS IN CARRY
FA20 E80BOO 5408
CALL
WRITE_BIT
;WRITE DATA BIT
FA2:3 90
54 •• POPF ,RESTORE CARRY FOR CRC CALC
FA24 E82400
541. CALL CRC_GEN ,CQt1PUTE CRC ON DATA BIT
FA27 FEC9 5411
DEC
CL flOOP TILL All 8 BITS DONE
FA29 75F2 5412 JHZ
"27
; JUMP IF NOT DONE YET
FA2B 58 5413 POP AX
;RESTORE REGS AX.CX
FA2C 59
5414
POP CX
A-73