IBM 5150

LOC OBJ
LINE SOURCE
f93C E421 5481
IN
AL, 021H
; RE_ENABLE INTERRUPTS
F93E
24fE 5482 AND AL. OFFH- 1
F940 E621 5483
OUT 021H. AL
F942 E845FF
5484
CALL
HOTOR_OFF
, TURN OFF MOTOR
F945 58 5485
pop AX , RESTORE RETURN CODE
F946 BOFcol 5486 CHP AH,OIH
, SET CARR't IF ERROR IAH>O)
F949 FS 5487 eHe
f94A C3 5488
RET
; FINISHED
5489 READ_BLOCK
ENDP
5490 ; - ---------------- - - - ---------------- - ---
5491 ; PURPOSE:
5492 TO READ A BYTE FROM CASSETTE
5493 , ON EXIT
5494 REG AL CONTAINS READ DATA BYTE
5495 i ------ -- ------------------- -------------
F94B 5496
READ.BYTE PROC NEAR
f94B S3 5497
PUSH BX
; SAVE REGS BX,CX
F94C 51 5498
PUSH cx
F94Q BI08
5499
HOV CL.8H
, SET BIT COUNTER FOR 8 BITS
F94F
5500
; eYTE-ASH
F94F 51
5501
PUSH CX
; SAVE ex
5502 ; ---------. ------------------- ---
5503 I READ DATA BIT FROM CASSETTE
5504 ; --------------------------------
f9S0 E62600 5505
CALL READ.HALF .BIT
; READ ONE PULSE
F953 E320
5506
JCXZ 10121
J IF c:X=O THEN TIMEOUT
5507
; BECAUSE OF NO DATA TRANSlTIOHS
f95S S3
5508 PUSH ex
; SAVE 1ST HALF BIT'S
5509
; PULSE WIDTH I IN ex)
F956 E82000 5510
CALL READ.HALF _BIT
, READ COMPLEMENTARY PULSE
F959 56
5511 POP AX
j COMPUTE DATA BIT
F95A E319
5512 JCXZ Wli
I IF c:X=O THEN TIMEOUT DUE TO
5513
; NO DATA TRANSITIONS
F95C 03D8
5514
ADD BX,AX
, PERIOD
f95E 61FBF006
551S eHP BX, 06FOH ; CHECK fOR ZERO BIT
F962 FS 5516 eHe I CARRY IS SET IF ONE BIT
F963 9f 5517 LAHF ; SAVE CARRY IN AH
F964 59 5518
POP CX
; RESTORE CX
5519 j NOTE:
5520
MS BIT OF BYTE IS READ FIRST.
5521 REG CH IS SHIFTED LEFT WITH
5522
,
CARRY BEING INSERTED INTO LS
5523 BIT OF CH.
5524 i AFTER ALL 8 BITS HAVE BEEN
5525 REAO,
THE HS BIT OF THE DATA BYTE
5526 WlLL BE IN THE MS BIT OF REG CH
F965 0005 5527
Rel i ROTATE REG CH LEFT WITH CARRY TO
5528
LS BIT OF REG CH
F967 9E
5529
SAMF ; RESTORE CARRY FOR CRC ROUTINE
f968 E60900
5530
CALL CRC.GEN
i GENERATE CRC fOR BIT
F96B FEe9
5531
DEC CL
;
LOOP TILL All 8 BITS OF DATA
5532
;
AssrHBLED IN REG CH
F96D
75EO
5533
JNZ WI9
I BYTE_ASH
F96F 8ACS
5534
MOV AL,CH
I
RETURN DATA BYTE IN REG Al
F971 Fe
5535
ele
F972
5536 10120:
; RD-BYT-EX
f972 59
5537
POP ex ; RESTORE REGS CX,BX
F973 58
5538
POP ox
F974 C3
5539
RET ; FINISHED
F975
554. N21 :
I NO-OATA
F97S 59
5541
POP
ex
;
RESTORE CX
F976 F9
5542 STe
I INDICATE ERROR
F977 f8F9
5543
JHP
"2.
I RD_BYT_EX
5544
READ_BYTE
ENOP
5545 ; ----------------- ------------------------ __ • ___ _
5546 j PURPOSE:
5547 TO COMPUTE TIHE TILL NEXT DATA
5548 TRANSITION (EDGE)
5549 i ON ENTRY:
5550 EDGE_CNT CONTAINS LAST EDGE CCIU'IT
5~51 ; ON EXIT:
5552 AX CONTAINS OLD LAST EDGE COUNT
5553 BX CONTAINS PULSE WIDTIi (HALF BIT)
5554 ; ----------------------------------- - - -----------
F979
5555
READ_HALF .BIT PRoe NEAR
f979 896400
5556
NOV CX, 100 I SET TIME TO WAIT FOR BIT
F97C 8A266800
5557
HOV I GET PRESENT INPUT VALUE
System BIOS 5-105