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Advanced Information Sheet
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:
• 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
• 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.
A block diagram is shown in Figure 1.
Functional Block Diagram
8 BIT INTERNAL
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