Diamond Systems RUBY-MM-1612 82C55 Digital I/O Chip Operation, 82C55 Register Map, Definitions

8. 82C55 DIGITAL I/O CHIP OPERATION

This is a short form description of the 82C55 digital I/O chip on the board. A full datasheet is included at the back of this manual.

82C55 Register Map
Base + n, Dir, Function	D7	D6	D5	D4	D3	D2	D1	D0
4, R/W, Port A	A7	A6	A5	A4	A3	A2	A1	A0
5, R/W, Port B	B7	B6	B5	B4	B3	B2	B1	B0
6, R/W, Port C	C7	C6	C5	C4	C3	C2	C1	C0
7, W, Config Register	1	ModeC	ModeA	DirA	DirCH	ModeB	DirB	DirCL

Configuration Register

The configuration register is programmed by writing to Base + 7 using the format below. Once you have set the port directions with this register, you can read and write to the ports as desired.

Bit No.	7	6		5	4	3		2	1	0
Name	1	ModeC		ModeA	DirA	DirCH		ModeB	DirB	DirCL
Definitions:
1	Bit 7 must be set to 1 to indicate port mode set operation.
DirA	Direction control for bits A7 – A0: 0 = output, 1						= input
DirB	Direction control for bits B7 – B0: 0 = output, 1						= input
DirCL	Direction control for bits C3 – C0: 0 = output, 1 = input
DirCH	Direction control for bits C7 – C4: 0 = output, 1 = input
ModeA, ModeB, ModeC			I/O Mode for each port, 0 or 1

Here is a list of common configuration register values (others are possible):

Configuration Byte
Hex	Decimal	Port A	Port B	Port C (both halves)
9B	155	Input	Input	Input	(all ports input)
92	146	Input	Input	Output
99	153	Input	Output	Input
90	144	Input	Output	Output
8B	139	Output	Input	Input
82	130	Output	Input	Output
89	137	Output	Output	Input
80	128	Output	Output	Output	(all ports output)

Copyright 2001 Diamond Systems Corp. Ruby-MM-1612 User Manual V1.1 P. 12