Keithley 194 Instruction Manual page 132

IEEE-488 PROGRAMMING
The general format of the status byte is shown in Figure
4-13. Note that most bits correspond to the bits in the SRQ
mask, as described above. These bits flag the following
conditions:
SRQ (bit 6)-This bit will be set if the service request was
generated by the Model 194. If bit 6 is cleared, other in-
struments on the bus should be checked to determine
where the SRQ occurred.
Error (bit 5)-This bit will be set if one of the following er-
rors has occurred:
1. An illegal device-dependent command (IDDC) or illegal
device-dependent command option (IDDCO) was
received.
2. The instrument was programmed with the REN line
false.
3. A trigger overrun has occurred.
4. The unit failed the self test.
5. A channel 2 command was received with no channel
2 A/D module installed.
6. The waveform may bc invalid.
7. A mode change was attempted with the unit in the dual-
channel display mode.
8. A Translator error has occurred.
9. A sample or delay conflict has occurred.
Note that the exact nature of the error can be determined
by using the Ul status command, as described in
paragraph 4.9.15. Reading Ul will clear the error bits in the
error status word and the error bit in the serial poll byte.
Ready (bit 4)-S& when the unit has processed all previous
commands and is ready to accept additional commands
over the bus. Cleared when the instrument is processing
commands.
Reading Done (bit 3)-S& when a reading is ready to be
sent over the bus. Cleared by requesting a reading over
the bus.
Button Pressed (bit 2)-S& when a front panel button has
been pressed (even if the unit is in remote). Cleared when
the UO status word is read.
Data Conditions (bit l)-Set when any bit in the data status
word is set. The exact nature of this condition can be deter-
mined by reading U2 status, as described in paragraph
4.9.15. Reading the U2 word clears this bit
Reading Overflow (bit 0)-Set when an overrange input
is applied to the instrument. Cleared when an on range
reading requested from the instrument. Note that it may
be necessary to reprogram the range or r&rigger a
measurement to get an on range reading.
NOTES
1. The status byte should be read cmce the instrument has
generated an SRQ in order to clear the SRQ line.
2. All bits in the status byte will be latched when an SRQ
is generated.
3. The status byte can bc read to determine current instru-
ment conditions even if SRQ is disabled.
4. If an error occurs, bit 5 (error) will remain latched until
the Ul status word (paragraph 4.9.15) is requested.
5. If the corresponding data condition occurs, bit 1 will re-
main latched until the U2 status word is read.
HP-85 Programming Example-Enter and run the program
below to demonstrate SRQ and status byte programming.
COMMENTS
Dimension string.
Place instrument in
remote.
Program for SRQ on
error.
Attempt to program
illegal command.
Get bus status.
If no SRQ, go back
and wait.
Serial poll the 194.
Identify the bits.
Loop eight times.
Display the status byte
bits.
Program for Ul status.
Get Ul status to clear
error.
Display Ul status.
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4-42