View/Change the State of GPIB Data and Control Lines

You can view or change the state of the GPIB data and control lines from within the Bus Monitor window.

The state of the GPIB data and control lines is displayed on the row of LEDs and the upper ASCII and Hex edit controls. You can alter the value of the GPIB data and control lines using the row of binary switches and the lower ASCII and Hex edit controls.

You can enter the GPIB data value as an ASCII value in the ASCII edit control, a hexadecimal value in the Hex edit control, or a binary value in the 8 to 1 binary switches. Note that the GPIB data value is replicated in all three representations: ASCII, hexadecimal, and binary.

You can enter the GPIB control value using the EOI, ATN, SRQ, REN, IFC, NRFD, NDAC, and DAV binary switches. The up position corresponds to the assertion of the line.

To accept a byte of data on the bus, use the NRFD and NDAC binary switches to simulate the IEEE 488 handshake, or use the Accept Byte button, which automatically toggles NRFD and NDAC in the correct sequence. The Accept Byte button is enabled by clicking the Enable Accept Byte button.

If you are using the Bus Monitor to assert GPIB lines, do not use the NI-488.2 ibfind or ibdev functions. These functions will unassert the lines on the bus, even though the switches in the Bus Monitor window show that the lines are asserted. If you encounter this problem, click the Unassert Lines button and avoid using the ibfind or ibdev functions.