IEEE-488 Programming
5-27
Serial poll byte
The general format of the serial poll byte is shown in Figure 5-15. Note that all bits except for
bit 6 correspond to the bits in the SRQ mask. These bits flag the following conditions:
Matrix ready (bit 3) — Set whenever the Matrix Ready signal is asserted. Cleared by the start of
relay switching.
Ready for trigger (bit 4) — Set when the Ready signal is asserted. This bit is cleared by:
1. Receipt of X. Start of relay switching.
2. Front panel keypress on master unit.
3. Changing Make/Break or Break/Make row.
4. Performing self-test.
Error (bit 5) — Set if an error condition occurs. Cleared by reading the U1 error status word
(paragraph 5.9.20).
SRQ (bit 6) — Set if the Model 708A requests service via the SRQ line; cleared by a serial poll.
Programming notes
1. The serial poll byte should be read once the instrument has generated an SRQ to clear the SRQ
line.
2. All bits in the serial poll byte latch when the instrument generates an SRQ.
3. If an error occurs, bit 5 (error) in the serial poll byte latches and remains so until the U1 word
is read (paragraph 5.9.20).
4. Multiple error conditions can be programmed by adding up the individual command values.
For example, send M12X for SRQ under matrix ready and digital I/O interrupt conditions.
Example
PRINT #1, "CLEAR 18"
PRINT #1, "REMOTE 18"
' Program for SRQ on error
PRINT #1, "OUTPUT 18;M32X"
' Attempt to program invalid option
PRINT #1, "OUTPUT 18;A2X"
' Check interface status
WAITSRQ:
IF NOT(srq%()) THEN GOTO WAIT SRQ
' Wait for SRQ to occur
PRINT #1, "SPOLL 18"
' Serial poll the instrument
INPUT #2, S
' Read serial poll byte
PRINT "B7 B6 B5 B4 B3 B2 B1 B0"
' Label the bit positions
FOR I=7 TO 0 STEP-1
' Loop eight times
PRINT BIT (S,I);
' Display the bit positions
NEXT I
PRINT #1, "OUTPUT 18;U1X"
' Program for error status
PRINT #1, "ENTER 18"
' Get U1 status to clear error
LINE INPUT #2, ERROR$
PRINT ERROR$
' Display error status
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