Tandy 1000 Programmer's Reference Guide

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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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200