National Instruments GPIB-BUF - Manual (Page 29)

Chapter 3 Technical Information
© National Instruments Corp. 3-7 GPIB-BUF User Manual
Internally, the local Individual Status (ist) bit of the GPIB-BUF is reset to 0
when the internal data buffer is empty of data. It is set to 1 when the
internal data buffer is not empty.
Therefore, after the GPIB Controller configures the GPIB-BUF with a
Parallel Poll Enable (PPE) message from 60 to 67 hex, the GPIB-BUF,
during a parallel poll, drives the data line (which the Controller has
specified) active when the internal data buffer is empty. When data is
present in the GPIB-BUF, it drives the data line inactive. Likewise, after
the GPIB Controller configures the GPIB-BUF with a PPE message from
68 to 6F hex, the GPIB-BUF, during a parallel poll, drives the data line
(which the Controller has specified) active when the internal data buffer is
not empty of data. When the internal data buffer is empty, it drives the data
line inactive. The possible parallel poll responses from the GPIB-BUF are
summarized in Table 3-1.
Unlike serial polls, you can parallel poll the GPIB-BUF even when it is in
listen-only mode.
Table 3-1. Parallel Poll Responses
PPE GPIB Data Line Driven Active
(hex) in Response to Parallel Poll
Buffer Empty Buffer Not Empty
60 DIO1 NONE
61 DIO2 NONE
62 DIO3 NONE
63 DIO4 NONE
64 DIO5 NONE
65 DIO6 NONE
66 DIO7 NONE
67 DIO8 NONE
68 NONE DIO1
69 NONE DIO2
6a NONE DIO3
6b NONE DIO4
6c NONE DIO5
6d NONE DIO6
6e NONE DIO7
6f NONE DIO8