Polling the gpib-buf, Figure 3-1. serial poll status byte, Polling the gpib-buf -5 – National Instruments GPIB-BUF User Manual
Page 27: Figure 3-1. serial poll status byte -5
Chapter 3
Technical Information
© National Instruments Corp.
3-5
GPIB-BUF User Manual
Polling the GPIB-BUF
The GPIB-BUF can return status information to the GPIB Controller
through the serial poll response byte as shown in Figure 3-1. This byte
contains two bits of information that reflect the current condition of the
GPIB-BUF data buffer and whether the GPIB-BUF is asserting the SRQ*
signal on the GPIB IN port. The serial poll status byte is returned as
follows:
7
6
5
4
3
2
1
0
SRQ
0
0
0
0
0
0
bit
empty
0 = not asserting SRQ*
0 = buffer is not empty
1 = asserting SRQ*
1 = buffer is empty
Figure 3-1. Serial Poll Status Byte
The empty bit always reflects the current status of the buffer while the SRQ
bit only returns a 1 if the GPIB-BUF is asserting the SRQ* signal line. The
GPIB-BUF asserts the SRQ* signal if the buffer is currently empty and the
SRQ-on-empty function is enabled by Switch 3 of U38. The GPIB-BUF
unasserts the SRQ* signal when the buffer is no longer empty or when the
GPIB Controller serial polls the GPIB-BUF. Although serial polls are
usually in response to an SRQ condition, the GPIB-BUF can be serial
polled at any time for any reason.
Note:
The GPIB-BUF cannot return a serial poll status byte if it is in
listen-only mode.