IBM 5150 - Page 264

LOC OBJ
LINE SOURCE
F936 7403 5194
JZ
W17
JUtlP IF TOO MANY RETRIES
F938 E962FF 5195
JMP W4
JUMP IF NOT TOO MANY RETRIES
F938
5196
10117: NO VALID DATA FOUND
5197 j------ NO DATA FROM CASSETTE ERROR, I.E. TIMEOUT
5198
F938
5E 5199 POP
51
RESTORE REGS
F93C 59 5200 POP
CX
lRESTORE REGS
~
F93D 58 5201
POP
BX
F93E 2B02
5202
SUB
OX,OX
,ZERO
NUMBER OF BYTES READ
F940 8404
5203
HOV
AH,04H
; TIME OUT ERROR I NO LEADER)
F942 50 5<:04 PUSH AX
F943 5205 10118: 1 HOT-OFF
F943
E421 5206
IN Al. 021H
; RE_ENABlE INTERRUPTS
F945 24FE 5207
AUO Al.
OFFH- 1
F947 E621 5208 OUT
021H. Al
F949 E842FF
5209
CAll
MOTOR_OFF
;
TURN OF F MOTOR
F94C 58
5210 POP AX
;RESTORE RETURN CODE
F94D 80FCOI 5211
CHP
AH,OlH
; SET CARRY IF ERROR (AH>O 1
F950 F5 5212 CHC
F951 C3
5213 RET iFItUSHED
5214 READ_BLOCK
ENOP
5215 ; -----------------------------------------
F952 5216
PROC NEAR
5217 PURPOSE:
5218 TO READ A BYTE FROM CASSETTE
5219
5220
ON EXIT REG AL CONTAINS READ DATA BYTE
5221
F952
53 5222
PUSH BX
,SAVE REGS BX,CX
F953 51 5223 PUSH
CX
F954 BI08 52<:4 HOV CL,8H ; SET BIT COUNTER fOR 8 BITS
F956 5225
W19:
; BYTE-ASM
F956
51 5226
PUSH CX
;SAVE
CX
5227 ; - ---- - -- --- - ---- ------ - ---- ----- -- -------
5228 ; READ DATA BIT FROM CASSETTE
5229
;-----------------------------------------
~ F957 E82600
5230
CALL READ_HALF _BIT
;READ mlE PULSE
F95A E320 5231
JCXZ W21
;
IF CX=O THUI TIMEOUT
5232
;BECAUSE
OF NO OA TA TRANSITIONS
F95C 53
5233 PUSH
BX
;SAVE 1ST HALF BIT'S
523ft ;PULSE I-lJOTH (UI BXI
F95D E82000
5235
CALL READ_HALF _BIT
;READ COMPLEMENTARY PULSE
F960 58
5236 POP AX
;COMPUTE
OATA BIT
f961 E319 5237
JCXZ W21 ; If CX=O THEN TIMEOUT DUE TO
5238
;NO DATA TRANSITIONS
F963 0308
5239
ADO
BX,AX jPERIOO
F965 8lFBF006 5240
CHP
BX. 06fOH
;
CHECK FOR ZERO BIT
F969 F5
5241
CHC
, CARRY IS SET If ONE BIT
F96A 9F
5242
LAHF ;SAVE CARRY IN AH
F96B 59
5243
POP CX iRESTORE CX
5244
;NOTE:
5245
;
MS BIT OF BYTE IS READ FIRST.
5246
REG CH IS SHIFTED LEFT WITH
5247
CARRY BEING INSERTED INTO LS
5248 BIT OF CH.
5249
AFTER
ALL 8 BITS HAVE 8EEN
5250 READ, THE MS BIT (IF THE DATA BYTE
5251 WILL BE IN THE M5 BIT OF REG CH
F96C 0005
5252
RCl
CH,l iRorATE REG CH LEFT ~ITH CARRY TO
5253 LS BIT OF REG Oi
F96E 9E 5254
SAHF
;RESTORE CARRY FOR eRC ROUTINE
f96F E8D900 5255
CALL CRC_GEN
;GENERATE
CRC FOR BI r
F972 FEC9
5256
DEC Cl
; LOOP TILL ALL 8 BITS OF DATA
5257
;ASSEMBLED
IN REG CH
F974 75EO
5258
JNZ W19 ; BYTE_ASM
~ F9768AC5
5259
HOV
AL,CH
;RETURN DATA BYTE
IN REG AL
F978 F8
5260
Cle
F979 5261
10120: ; RD-BYT-EX
F979 59
5262 POP
ex
;RESTORE REGS CX,BX
F97A 58
5263 POP BX
F97B C3
5264
RET
;FINISHED
F97C
5265
10121 : ; NO-DATA
F97C
59
5266
POP
ex
iRESTORE
CX
F970 F9 5267
STC
; INDICATE ERROR
A-71