IBM 5150 - Page 196

LOC OBJ LINE SOURCE
5328
.----------------------------------------
5329 I PURPOSE:
53]0
TO TURN cASSEnE MOTOR OFF
5331
; ----- - -- - --- ------ -- ----- -- ------ -------
F88A £461 5332
IN U.PORT_B
; READ CASSETTE OUTP\IT
F8& OC08 5333
OR Al.OSH
i SET BIT TO TLRH OFF
FUE EBFS
5334 JHP
w'
i WRITE IT. CLEAR ERROR. RETURH
5335 I1OTOR_OFF ENDP
~
F890 5336
READ_BLOCK PRDC NEAR
5337
1- ---- -- ---- - -------- - - -- - - -- - ------ - - - - - - - ----------- - - - - -------
5338
J ~POSE:
5339 TO READ 1 OR MORE 256 BYTE BLOCKS FROM CASSETTE
5340
5341 I ON ENTRY:
5342 ES IS SEGMENT FOR MEtIORV BUFFER (FOR COtlPACT CODE)
5343
ex POINTS TO START Of MEHORY BUFFER
5344 ex COIiTAINS HUHBER OF BYTES TO READ
5345 , ON EXIT:
5346
ex POINTS 1 BYTE PAST LAST BYTE PUT IN ME"
5347 ex CONTAINS DECREMENTED BYTE COUNT
5348
OX CONTAINS NUt1BER OF BYTES ACTUALLY READ
5349
5350
CARRY FlAG IS CLEAR IF NO ERROR DETECTED
5351
CARRY FlAG IS SET IF CRC ERROR DETECTED
5352
;--------'----------------------------------------------.---------
FS9Q 53
5353
PUS"
ox J S ... VE 8X
FS9l 51
5354
PUS"
ex
, S"'VE CX
F892 56
5355
PUS"
51
J S",VE 51
F893 BE0700
5356
I10Il 51. 7
, SET
UP RETRY COUNT FOR LEADER
f8% E8BFOI
5357
CAlL BEGIN_OP
, BEGIN
BY STARTING MOTOR
F899
5358
W4,
, SEARCH FOR LEADER
F899 £462
5359
IN Al,PORT~C
I GET INTIAL VALUE
F898 2410
5360
ANO
"'L,OlOH
I I1ASK Off EXTRANEOUS BITS
F89D "'26800 5361
HOV LAST_V ... L .... L I S"'VE IN Loe LAST_VAL
F8AO BA7A3F
F8A3
5362
5363
... ,
HOV
OX.16250 ; I OF TRANSITIONS TO LOOK FOR
, WAIT]OR_EDGE
F8A3
F606710080
F8A8 7503
5364
5365
TEST
JHZ
BIOS_BREAK. 80H
....
; CHECK FOR BREAK KEY
I JUttP IF NO BREAK KEY
~
5366
I
JUt1P IF BREAK KEY HIT
F8A"
5367
NO'
F8A ... 4A
5368
DEC OX
F8AB 7503
5369
JNZ W7
I JUHP IF BEGINNING OF LEADER
F8AD
5370,
W6A:
F8AD £98400
, ...
5371
5372
..,7:
JHP
M17
, JUttP IF NO LEADER FOUl)
F8BO E8C600 5373
CALL READ_HALF _BIT I IGNORE FIRST EDGE
F8B3 ElEE
5374
JCXl
W5 I JUHP IF NO EDGE DETECTED
F8B5 BA7603
5375
I10Il DX.0378H
,
CHECK FOR HALF BITS
F8B8 890002 5376
HOV
CX,200H I MUST HAVE AT LEAST THIS ttAHY ONE SIZE
5377 I PULSES BEFORE CHCKNG FOR SYNC BIT (Q)
F6BB E421 5378
IN AL, 021H
I INTERRUPT
MASK REGISTER
F88D OCOI
5179 OR Al.I I DISABLE TIMER INTERRUPTS
F8BF E621 5380
OUT
021H. AL
'SCl
5381
we,
I SEARCH-LOR
Facl F606710OBO 5382
TEST BIOS_BREAK, 80H I CHECk FOR BREAK. kEY
F8C6 756C
'la'
JNZ
M17
I JUHP IF BREAK KEY HIT
F8C8 51
5384
PUS"
CX
; SAYE REG ex
F8C9 E8AoOO
5la.
CALL READ_HALF _BIT
I GET PULSE WIDTH
FacC OBC9
5386 OR CX. CX
, CHECK FOR TRANSITION
F6CE 59
'la7
pop
CX J RESTORE ONE BIT COUNTER
F8CF 74C8
5366
JZ
W4
, JUHP IF NO TRANSITION
F6Dl 3BD3 5389 CMP
DX,BX I CHECK PULSE WIDTH
F8D3 £304 5390
JCXZ M. I IF CX=O THEN WE CAN LOOK
5391
J FOR SYNC BIT (0)
FOO5 73C2
5392
JNt
W'
, JI.R1P IF ZERO BIT (NOT GOOD lEADER)
F6D7 E2E8
5393
LOOP W8 I DEC ex At-IJ READ ANOTHER HALF ONE BIT
F6D9
5394 W9:
I FIND-SYNC
F8D9 72E6
5395 JC
w.
I JU1P IF ONE BIT (STILL LEADER)
5396
~
5397
;----- A SYNCH BIT HAS BEEN FOUND •
READ SYN CHARACTER:
• n.
F8DB E89BQQ 5399
CALL READ_HAlF _BIT
I SKIP OrnER HALF OF SYNC BIT (0'
FOOE E86A00 5400
CALL
READ_BYTE I READ SYH BYTE
F8El Xl6 5401
CHP AL, 16H I SYHCHROHIZA TION CHARACTER
F8E3 7549 5,*02
JNE Wl0 i JUMP IF BAD LEADER FotNl.
5403
54 •• I-~--- GOOD CRe so READ DATA BLOCK{S'
System BIOS 5-103