The Intel 8255A is a general purpose 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 individually programmed in 2 groups of 1 and used in 3 major modes of operation.The 8255 is a 40 pin integrated circuit (IC), designed The 8255 is a 40 pin It designed by Intel for the 8080 microprocessor
Two control groups, labeled group A control and group B control define
how the three I/O ports operate. There are several different operating
modes for the 8255 and these modes must be defined by the CPU writing
programming or control words to the device 8255.
The line group of port C consists of two 4 bit ports. One of the 4 bit
group is associated with group A control and the other 4 bit group with
group B control device signals. The upper 4 bits of port C are associated
with group A control while the lower 4 bits are associated with group
B control.
The final logic blocks are read/write control logic and data bus buffer.
These blocks provide the electrical interface between the Z80 and the
8255.
The data bus buffer buffers the data I/O lines to/from the Z80 data bus.
The read/write control logic routes the data to and from the correct internal
registers with the right timing. The internal path being enabled depends
on the type of operation performed by the Z80. The type of operation can
be I/O read or I/O write.
Posted in 8255 microprocessor, 8255 programmable peripheral device, Architecture of 8255, Architecture of 8255 programmable peripheral device
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