Tandy 1000 Programmer's Reference Manual page 207

Chapter 6
I
BIOS Services
Transmit Character
Transmit (output) the character in AL (which is preserved).
Entry Conditions:
AH
=
1
AL
=
character to transmit
DX
=
port number (0 or 1)
Exit Conditions:
AH
=
RS-232 status; see Get Current Comm Status (AH
=
3)
below (If bit 7 is set, the routine was unable to transmit
the character because of a timeout error.)
Receive Character
Receive (input) a character in AL (wait for a character, if neces-
sary). On exit, AH will contain the RS-232 status, except that
only the error bits (1,2,3,4,7) may be set; the timeout bit (7), if
set, indicates that data set ready was not received. Thus, AH is
non-zero only when an error occurred.
Entry Conditions:
AH
=
2
DX
=
port number (0 or 1)
Exit Conditions:
AL
=
character received
AH
=
RS-232 status; see Get Current Comm Status (AH =3)
Get Current Comm Status
Read the communication status into AX.
Entry Conditions:
AH
=
3
DX
=
port number (0 or 1)
hP1nii)
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