Radio Shack TRS-80 Model II Reference Manual page 156

Modell! TRSDOS
SUBROUTINE FOR BASIC COMMUNICATIONS PROGRAM
THIS ROUTINE
MusT
BE EXEClJIED
AI 300
BAIID
OR
HIGHER
XMITER
XMITt
ERAOR
BITEST
BITSTJ
oRG IilEF81ilH
INC DE
LD A, (DE)
LO L,A
INC DE
LD A, (DE)
LD H,A
LD A,(HL)
CP
0
,JR
NZ,XMITER
LD A,90
RST 8
JR
C,ERRoR
RET NZ
DR
A
JR NZ,ERAOR
LD (HL),B
RE':I
LD B,A
LD DE,IilFFFFH
LD A,97
RST 8
JR C ,ERROR
NoP
NoP
RET
Z
BIT 0,A
JR NZ , ERROR
LD A,D
OR
E
DEC DE
JR NZ, XMITl
LD (HL) ,00
10
B,8
LD HL,BITST3
BIT 7,A
LD
(HL)
I
'Iil'
JR
Z ,BITSTl
INC
(HL)
RLCA
INC
HL
DJNZ
BlTEST
LD HL.BITST2
LD B,l •
LD C,
.....
LP A,9
RST
8
RET
ION ENTRY DE POINTS TO A 3 BYTE STRING DESCRIPTOR
IDE NOW POINTS TO LSB OF STRING ADDDRESS
ILSB OF STRING ADDRESS TO ACCUMULATOR
ILSB of STRING ADDRESS TO REGISTER L
IDE NOW POINTS TO MSB OF STRING ADDRESS
I MSB OF STRING ADDRESS TO ACCUMULATOR
IMSB OF STRING ADDRESS TO REGISTER H
11 BYTE STRING TO ACCUMULATOR
ISEE IF CHARACTER IS ZERO
IIF NOT ZERO TRANSMIT CHARACTER, ELSE FALL THROUGH TO RECIEVE CHARACTER
ISVC CALLIPORT A RECIEVE
I
10UIT ON ERROR IF MODEM CARRIER NOT PRESENT
IRETURN IF
r-tJ
CHARACTER RECIEVED
ISET sTATUS BITS
IQ\JIT ON ERROR IF ANY STATUS BITS ARE SET
IPASS RECIEVEP CHARACTER TO STRING LOCATION
ICHARACTER TO BE TRANSMITTED Tn REGISTER B
ILooP COUNT IF TRANSMITER BUSY STATUS ENCOUNTERED
ISVC CALLIPoRT A TRANSMIT
I
10UIT ON ERROR IF MODEM CARRIER NOT PRESENT
I INSERT .llLD (HL), 00" HERE WHEN USING MODEM IN HALF-DUPLEX MODE
I
IRETURN IF CHARACTER TRANSMITTED
ICHECK CLEAR TO SEND STATUS BIT
10UIT ON ERROR IF STATUS BIT SET
I MS8
of
LOOP COUNT TO ACCUMUL ATOR
ILSB OF LOOP COUNT
IREDUCE LOOP COUNT
ILoOP IF COUNT IS NOT ZERO, ELSE FALL THROUGH
10
AN
ERROR
100 NoT DISPLAY CHARACTER IF ERROR ENCOUNTERED
ILOOP COUNT (8 BIT STATUS BYTE)
ISTORAGE AREA
ICHECK BIT 7 OF ACCUMULATOR FOR COMMUNICATIONS STATUS
ILOAD ASC II ZERO
IJUMP
IF
STATUS BIT NOT SET
IASC-II ZERO ~> Ase-II ONE IF STATUS BIT SET
IROTATE ACCUMULATOR LEFT
IMOVE TO NEXT STORAGE POSITION
ILoOP TO CHECK STATUS OF
8
BITS
IERROR MESSAGE Tn BE
DISPI
AYFD
ILENGTH OF MESSAGE
ICHARACTER TO BE INSERTED AT THE END
OF
ERROR MESSAGE
ISV-C CALLI VIDEO LINE
BITST2
BITST.3
192
OEFM
OEFS
I ERROR MESSAGE
ISToRAGE AREA FOR ERROR STATUS BITS TO BE DISPLAYED