Tandy 1000 Technical Reference Manual

Tandy 1000
inter
Technical Reference Manual
8255A18255A·5
Figure 7. Bit Set/Reset Format
Operating Modes
MODE 0 (Basic InpuIlOutput). This functional configura-
tion provides simple input and output operations for
ea.;h of the three ports. No "handshaking" is required,
data is simply written to or read from a specified port.
When Port C is being used as status/control for Port A or B,
these bits
can be set or reset by using the Bit Set/Reset op-
eration just
as if they were data output ports_
Interrupt Control Functions
When the 8255A IS programmed to operate In mode 1 or
mode 2, control signals are provided that can be used as
interrupt request inputs to the CPU. The interrupt re-
Quest
signals, generated from port C, can be inhibited or
enabled by setting or resetting the associated INTE flip-
flop, using the bit set/reset function of port C.
This function allows the Programmer to disallow or allow a
specific
I/O device to interrupt the CPU without affecting
any other device in the
interrupt structure.
INTE flip-flop definition:
(BIT-SETI - INTE is SET - Interrupt enable
(BIT-RESET) -
INTE is RESET - Interrupt disable
Note:
All Mask flip·flops are automatically reset during
mode selection and device Reset.
Mode 0 Basic Functional Definitions:
I Two 8-bit ports and two 4-bit ports.
I Any port can be input or output.
I Outputs are latched.
• Inputs
are not latched.
• 16
different Input/Output configurations are possible
in this Mode.
___________ ----" -~-- '
AA
~~~-l,------------
M ~~ ~~
'-- ...J
1
_______ ---" r-Ir--_"A_+- -+--_'HA_---,l"i ~------
_____ ...... r-------Ir-_
'A
_"'_.--_.- -+ -+--_-_--=-'_AA==~"I r------
CS,Al.AO
MODE 0 (Ballc Input)
MODE 0 (Bille Output)
6·170

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