User's Manual

Lab-NB User Manual 4-56 © National Instruments Corporation

Mode 0–Basic I/O

This mode is for simple I/O operations for each of the ports. No handshaking is required; data is

simply written to or read from a specified port.

Mode 0 has the following features:

• Two 8-bit ports (A and B) and two 4-bit ports (upper and lower nibble of port C).

• Any port can be input or output.

• Outputs are latched, but inputs are not latched.

Mode 1–Strobed I/O

This mode is used for transferring data with handshake signals. Ports A and B use the eight lines

of port C to generate or receive the handshake signals. This mode divides the ports into two

groups (group A and group B).

• Each group contains one 8-bit data port (port A or port B) and one 4-bit control/data port

(upper or lower nibble of port C).

• The 8-bit data ports can be either input or output, both of which are latched.

• The 4-bit ports are used for control and status of the 8-bit data ports.

• Interrupt generation and enable/disable functions are available.

Mode 2–Bidirectional Bus

This mode is for communication over a bidirectional 8-bit bus. Handshake signals can be used

in a manner similar to mode 1. Interrupt generation and enable/disable functions are also

available. Other features of this mode include the following:

• Used in group A only (port A and upper nibble of port C).

• One 8-bit bidirectional port (port A) and a 5-bit control status port (port C).

• Both inputs and outputs are latched.

Single Bit Set/Reset Feature

Any of the 8 bits of port C can be set or reset with one control word. This feature is used to

generate status and control for port A and port B when operating in mode 1 or mode 2.