D8255
Programmable Peripheral Interface
ver 1.00
OVERVIEW
The D8255 is a programmable I/O device
which is designed for use with all Intel and
most other microprocessors.
It provides 24 I/O pins which may be indi-
vidually programmed in 2 groups of 12 and
used in 3 major modes of operation:
●
Mode 0 - Basic Input/Output.
This func-
tional configuration provides simple input
and output operations for each of the
three ports. No „handshaking'' is required,
data is simply written to or read from a
specified port. Mode 0 Basic Functional
Definitions:
○
Two 8-bit ports and two 4-bit ports.
○
Any
○
16
○
The 8-bit data port can be either input or out-
put Both inputs and outputs are latched.
○
The 4-bit port is used for control and status of
the 8-bit data port.
●
MODE 2 - Strobed Bidirectional Bus I/O.
This functional configuration provides a
means for communicating with a periph-
eral device or structure on a single 8-bit
bus for both transmitting and receiving
data (bidirectional bus I/O). „Handshak-
ing'' signals are provided to maintain
proper bus flow discipline in a similar
manner to MODE 1. Interrupt generation
and enable/disable functions are also
available. MODE 2 Basic Functional Defi-
nitions:
○
Used in Group A only.
○
One 8-bit, bi-directional bus port (Port A) and
port can be input or output
.
different Input/Output configurations
are possible in this Mode
a 5-bit control port (Port C).
○
The 5-bit control port (Port C) is used for con-
●
MODE 1 - Strobed Input/Output. This
functional configuration provides a means
for transferring I/O data to or from a
specified port in conjunction with strobes
or „handshaking'' signals. In mode 1, Port
A and Port B use the lines on Port C to
generate or accept these „handshaking''
signals. Mode 1 Basic functional Defini-
tions
:
○
Two Groups (Group A and Group B).
○
Each group contains one 8-bit data port and
trol and status for the 8-bit, bi-directional bus
port (Port A)
The functional configuration of the D8255 is
programmed by the system software so that
normally no external logic is necessary to
interface peripheral devices or structures.
The control word register can be both written
and read as shown in the address decode
table in the pin descriptions.
one 4-bit control/data port.
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