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CMSC 391 -- Programming Microcontrollers |
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82C55 Info
Early day peripheral chips are now used to control the I/O functions that are now
inside the microcontroller. Now they support the microcontroller. The 8051 losses two
parallel I/O ports when used with external memroy, part of a third to serial data
communications and interrupt functions. The 8255 makes up for these loses.
The 8255 is packaged as a 40-pin DIP. and features three 8-bit programmable parallel I/O prots
named A, B, and C. (Our board has two 82C55s, and keeps that straight by calling the second
set D, E, and F. We used port_e with the LEDs.)
These ports can be programmed in one of three modes:
- Mode 0 -- Basic I/O: Data written to the port is latched, data read from the port
is read from the input pins. (This mode is identical to 8051 port operation.)
- Mode 1 -- Strobed I/O: This handshaking mode uses ports A and B is I/O and port C
to generate handshaking signals to the devices connected to ports A and B and an
interrupt signal to the host microcontroller.
- Mode 2 -- Strobed bi-directional I/O: This mode is similar to mode 1 with the ability
to use port A as a bi-directinal data bus.
PRJC
©2004, Gary L. Burt