Radio Shack TRS-80 Model II Reference Manual page 250

Modell! TRSDOS
Exit Conditions
B
NZ
flag
C
flag
A
BIT
o
1
2
3
4
5
6
7
Character found, if any.
No character found (check communications status).
Modem carrier was not present when
SYC
was entered.
Communications status:
MEANING WHEN SET
Not used.
Not used.
Not used.
Modem carrier not present.
Parity error occurred on last character received (in register B).
Data lost due to overflow (register B contains last character).
Framing error occurred on last character received.
A break sequence (extended null character) has been received.
ATX
BTX
Channel AlB Transmit (function codes
97/99)
These routines perform character output to channel
A
or
B.
They are analogous to
video character output (see
YDCHAR).
TRSDOS
sets up
A/BTX, A/BRCY
and
A/BCTRL
when you initialize channel
AlB
with
RS232C.
If you call any ofthese routines while the channel is not initialized (active),
you will get an error return code of
I
(no function code exists).
Data bytes will be transmitted even if no carrier is present. You must check the
status flags and register
A
for error conditions. Carry flag set means that no carrier
was present. You may ignore this flag if your application does not" care" whether
the carrier is present during transmission.
Register
A
contains status information upon return from this
SYC.
Entry Conditions
A
A
B
286
97
(for
ATX)
99
(for
BTX)
ASCII
code for character to be sent