User's Manual

Chapter 4 Register-Level Programming

Mode 1 Output Programming Example

Example 1. Configure port A as an output port in mode 1:

• Write A0 (hex) to the Digital Control Register.

• Wait for bit 7 of port C (OBFA*) to be cleared, indicating that the data last written to port A

has been read.

• Write new data to port A.

Example 2. Configure port B as an output port in mode 1:

• Write 84 (hex) to the Digital Control Register.

• Wait for bit 1 of port C (OBFB*) to be cleared, indicating that the data last written to port B

has been read.

• Write new data to port A.

Mode 2 Control Words

In mode 2, an 8-bit bus can be used for both input and output transfers without changing the

configuration. The data transfers are synchronized with handshaking lines in port C. This mode

uses only port A; however, port B can be used in either mode 0 or mode 1 while port A is

configured for mode 2.

The control word written to the Digital Control Register to configure port A as a bidirectional

data bus in mode 2 is shown below. Because mode 2 is for port A only, port B can be

programmed to operate in mode 0 or mode 1. If port B is configured for mode 0, then PC2, PC1,

and PC0 of port C can be used as extra input or output lines.

Port C

(PC2-PC0)

1 = input

0 = output

Port B direction

1 = input

0 = output

Group B Mode

0 = mode 0

1 = mode 1

1 X X 1/01 1/0X 1/0

765

43210

During a mode 2 data transfer, the status of the handshaking lines and interrupt signals can be

obtained by reading port C. The port C status-word bit definitions for a mode 2 transfer are

shown next.