Tandy 1000 Technical Reference Manual

Tandy 1000
Mode Definition Summary
8255A/8255A·5
Technical Reference Manual
MOOED
PAO
~~u--I-%cT=
I
PAl
IN
I
OUT
PA2
IN
I
OUT
PA3
IN
I
OUT
PA4
IN
I
OUT
PAS
IN
i OUT
PA6
IN
I
OUT
PA7
IN
OUT
PBO
IN
OUT
PBI
IN OUT
PB2
IN
OUT
PB3
IN OUT
PB4
IN
OUT
PBS
IN OUT
PB6
IN
OUT
PB7
IN OUT
PCO
IN OUT
PC,
IN OUT
PC2
IN OUT
PC3
IN
OUT
PC4
IN
OUT
PCS
IN OUT
PC6
I
IN OUT
PC]
IN OUT
MODEl MODE 2
-;~-=r-6~
GROUPAONLY
~---- ---- ---
-
IN ,OUT
-
IN
i
OUT
--
IN OUT
--
IN
OUT
IN OUT
--- IN
OUT
---
IN OUT
--
IN OUT
IN OUT
IN
OUT
IN OUT
MODE a
IN OUT
OR MODE 1
IN OUT
ONLY
IN OUT
IN OUT
INTRB INTRB
I/O
IBFB OBFB
I/O
STBB
ACI<B
I/O
INTRA INTRA INTRA
STBA
I/O
STBA
IBFA
I/O IBFA
I/O
ACKA ACKA
I/O
:
OBFA
OBFA
Special Mode Combination Considerations
There are several combinations 01 modes when not all of the
bits in Port C are used for control or status. The remaining
bits can be used as follows:
If
Programmed as Inputs -
All
input lines can be accessed during a normal Port C
read.
If Programmed as Outputs-
Bits in C upper (PCrPC4) must be individually accessed
using
the bit set/reset function.
Bits in Clower (PC3'PCO) can be accessed using the bit
set/reset function or accessed as a threesome by writing
into Port C.
Source Current Capability on Port B and Port C
Any set of ~ output buffers, selected ranaomly from
Ports Band C can source lmA at 1.5 volts. This feature
allows the 8255 to directly drive Darlington type drivers
and high-voltage displays that require such source current.
Reading Port C Status
In Mode 0, Port C transfers data to or from the peripheral
device. When the 8255 is programmed to function in Modes
1 or 2, Port C generates or accepts "hand-shaking" signals
with
the peripheral device. Reading the contents of Port C
allows
the programmer to test or verify the "status" of each
peripheral device and change the program flow accordingly.
There is no special instruction to read the status informa-
tion from Port C. A normal read operation of Port C is
executed to perform this function.
INPUT CONFIGURATION
07 06 DO) 04 [)l 02 01 Do
1
1
"0
i 110 IIBFA jlNTf
A
jINTRAjINTE
H
! IBF(1 ilNTRFlI
OUTPUT CONFIGURATION
D , 06 05 04 D
3
D
2
D
1
00
IOBFA[INTEAI"o 11/0 IINTRAliNTE,(OBF,I'NTR,1
Figure 17. MODE 1 Status Word Format
(DEFINED BY MODE. 0 OR MODE 1 SELECTIONI
Figure 18. MODE 2 Status Word Format
6-179

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