Tandy 1000 Programmer's Reference Guide

Chawter 1 I System Calls
Notes:
This exit is taken only for disk errors occurring during
an Interrupt 21H. It is not used
for errors during In-
terrupts 25H
or 26H.
This routine is entered in a disabled state.
0 The SS, SP, DS, ES, BX, CX, and DX registers must
be reserved.
This interrupt handler should not use MS-DOS function
calls. If necessary, it can use calls OIH through OCH.
Use
of any other call will destroy the MS-DOS stack
and will leave MS-DOS in an unpredictable state.
0 The interrupt handler must not change the contents of
the device header.
If the interrupt handler has its own error management
routine, rather than returning
to MS-DOS, it should re-
store the application program’s registers from the stack,
remove all but the last
3 words on the stack, and then
issue an IRET. This will cause a return
to the pro-
gram immediately after the INT 21H that experienced
the error. Note that if this is done, MS-DOS will be in
an unstable state until
a function call higher than OCH
is issued.
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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