Tandy 1000 Technical Reference Manual

Tandy 1000
Technical Reference Manual
8255AJ8255A·5
APPLICATIONS OF THE 8255A
INTERRUPT
REQUEST
PC.
1
---
PC
5
-
FUllY
DECODED
KEYBOARD
PS
o
-8
0
PBl ----- 8
1
PB
2
----B,
PB3--~B3
PB", ---- B
4
PB
5
--- Be.
PBf; -----"- __ BACKSPACE
PB,
PC) PA
o
----
PAl --
PA
2
----
PA
3
-----
PA", -
PA
5
---
PA
6
-------
PA
J
.. --
MODE 1
IINPUT)
MODE 1
(OUTPUTI
The 8255A is a very powerful tool for interfacing
peripheral equipment to the microcomputer system. It
represents the optimum use of available pins and is flex·
ible enough to interface almost any I/O device without
the need for additional external logic.
Each peripheral device in a microcomputer system
usually has a "service routine" associated with it. The
routine manages the software interface between the
device and
the CPU. The functional definition of the
8255A
is programmed by the I/O service routine and
becomes an extension of the system software. By ex-
amining the I/O devices interface characteristics for
both data transfer and timing, and matching this infor-
mation to the examples and tables in the detailed opera·
tional
description, a control word can easily be devel·
oped
to initialize the 8255A to exactly "fit" the applica-
tion. Figures 19 through 25 present a few examples of
typical applications of the 8255A
INTERRUPT
REOUEST -
PC
l
....... DATA READY
PC
2
------
PC, -_ BLANKING
PC
o
PC] -.-------......- CANCEL WORD
PC, PA
o
PA,
PA,
PA,
PA,
INTERRUPT
REQUEST
Figure 20. Keyboard and Display Interface
PAc, ------,.
IQUTPUT'I PA6
PA,
PC
6
---
INTERRUPT
REOUEST
I
MODE 1
IOUTPUTI
PC,
PC. _FOHWARO'REV-
PB
O
PB,
PB,
PB,
PB,
PB,
PB
6
PB
l
----
PA 6 -----
PC, ---DATAREAOY
Pel --_ .. -
pc" --- -_ArK,NOVlLfDGE
Figure 19. Printer Interface
- -P~o ~ .. "--.lli1'" ~' .. '.' ..•..•... o ~ --',. HRM>N"
PB
l
- .'0---- -tADORfSS
es, ~ ._.- ~ n·---4
MOOF 0 PB
J
f---------- - b
PB
4
- ------ -----<1 -_ 'I}---- -1
::: ~- -- ---: ~ - -:- -1
PB/- -- - ----~- ':>---- -----1
L-_~--'-' +
Figure 21. Keyboard and Terminal Address
Interface
6-180

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