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IN82C55AN Datasheet(PDF) 3 Page - Integral Corp.

Part No. IN82C55AN
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Maker  INTEGRAL [Integral Corp.]
Homepage  http://www.iksemi.com/

IN82C55AN Datasheet(HTML) 3 Page - Integral Corp.

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The IN82C55AN is a programmable peripheral interface device designed for use in Intel microcomputer
systems. Its function is that of a general purpose I/O component to interface peripheral equipment to the
microcomputer system bus. The functional configuration of the IN82C55AN is programmed by the system
software so that normally no external logic is necessary to interface peripheral devices or structures.
Data Bus Buffer
This 3-state bidirectional 8-bit buffer is used to interface the IN82C55AN to the system data bus. Data is
transmitted or received by the buffer upon execution of input or output instructions by the CPU. Control
words and status information are also transferred through the data bus buffer.
Read/Write and Control Logic
The function of this block is to manage all of the internal and external transfers of both Data and Control or
Status words. It accepts inputs from the CPU Address and Control busses and in turn, issues commands to
both of the Control Groups.
Group A and Group B Controls
The functional configuration of each port is programmed by the systems software. In essence, the CPU
“outputs” a control word to the IN82C55AN. The control word contains information such as “mode”, “bit set”,
“bit reset”, etc., that initializes the functional configuration of the 82C55A. Each of the Control blocks (Group
A and Group B) accepts “commands” from the Read/Write Control Logic, receives “control words” from the
internal data bus and issues the proper commands to its associated ports.
Control Group A - Port A and Port C upper (C7 - C4)
Control Group B - Port B and Port C lower (C3 - C0)
The control word register can be both written and read as shown in the address decode table in the pin
descriptions. Figure 6 shows the control word format for both Read and Write operations. When the control
word is read, bit D7 will always be a logic “1”, as this implies control word mode information.
Ports A, B, and C
The IN82C55AN contains three 8-bit ports (A, B, and C). All can be configured in a wide variety of functional
characteristics by the system software but each has its own special features or “personality” to further
enhance the power and flexibility of the IN82C55AN.
Port A. One 8-bit data output latch/buffer and one 8-bit input latch/buffer. Both “pull-up” and “pull-down” bus
hold devices are present on Port A.
Port B. One 8-bit data input/output latch/buffer. Only “pull-up” bus hold devices are present on Port B.
Port C. One 8-bit data output latch/buffer and one 8-bit data input buffer (no latch for input). This port can be
divided into two 4-bit ports under the mode control. Each 4-bit port contains a 4-bit latch and it can be used
for the control signal outputs and status signal inputs in conjunction with ports A and B. Only “pull-up” bus
hold devices are present on Port C.
See Figure 4 for the bus-hold circuit configuration for Port A, B, and C.

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