ia8255 Innovasic Semiconductor Inc., ia8255 Datasheet - Page 2

• Manufacturer Part Number: ia8255
• Description: Programmable Peripheral Interface Adapter
• Manufacturer: Innovasic Semiconductor Inc.

Programmable Peripheral Interface Adapter
The IA8255 is a programmable peripheral interface adapter mega-function designed to be
functionally equivalent to the Intel 8255A and Harris 82C55A devices. This function has 24 I/O
signals programmable in two groups of 12. Three modes of operation allow the following:
A block diagram is shown in Figure 1.
Functional Block Diagram
Figure 1
IA8255
D7:D0
Basic Input/Output (Mode 0) - Port A, Port B, Port C (upper), and Port C (lower) can be
independently configured as inputs or outputs to read or hold static data. Outputs are
latched, but inputs are not latched.
Strobed Input/Output (Mode 1) - Port A and Port B can be independently configured as
strobed input or output buses. Signals from Port C are dedicated as control signals for data
handshaking.
Bidirectional Bus (Mode 2) - Port A can also be configured as a bidirectional bus, with the
majority of Port C providing the control signals. In this case, Port B is still capable of
implementing one of the previous described modes.
RESET
CS_n
RD_n
WR_n
A0
A1
REGISTER AND
CONTROL
DATA BUS
BUFFER
LOGIC
CONTROL
GROUP A
CONTROL
GROUP B
Copyright
Customer Specific IC Solutions
1999, InnovASIC Inc.
8 BIT INTERNAL
DATA BUS
Advanced Information
UPPER (4)
GROUP A
GROUP A
GROUP B
GROUP B
PORT A
PORT C
PORT C
LOWER
PORT B
(8)
(4)
(8)
PC7:PC4
PC3:PC0
PA7:PA0
PB7:PB0
I/O
I/O
I/O
I/O
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