Keithley 6512, Instruction Manual

Page: 65 / 156

IEEE-488 Programming
3-10
Figure 3-2
SRQ mask and status byte format
SRQ can be programmed by sending the ASCII letter “M” followed by a decimal number to set
the appropriate bit in the SRQ mask. Note that the instrument may be programmed for more than
one set of conditions simultaneously. To do so, simply add up the decimal bit values for the re-
quired SRQ conditions. For example, to enable SRQ under reading overflow and buffer full con-
ditions, send M3X.
Status Byte The status byte contains information relating to data and error conditions within the instrument.
The general format of the status byte (which is obtained by using serial polling) is also shown
in Figure 3-2. Note that the various bits correspond to the bits in the SRQ mask as described
above.
The bits in the status (serial poll) byte have the following meanings:
Reading Overflow (Bit 0)—Set when an over-range input is applied to the instrument. Cleared
when a non-overflowed reading is available.
Data Store Full (Bit 1)—Set when all 100 readings in the data store buffer have been stored.
Cleared by reading a stored reading over the bus (B1X).
Reading Done (Bit 3)—Set when the Model 6512 has completed the present reading conversion.
Cleared by requesting a reading over the bus.
Ready (Bit 4)—Set when the instrument has processed all previously received commands and
is ready to accept additional commands over the bus. Cleared when processing commands.
Error (Bit 5)—Set when an error condition occurs, as described above. Cleared by reading the
error word with the U1 command.
RQS (Bit 6)—Set if the Model 6512 has asserted SRQ. Cleared by serial polling the instrument.
Bits 2 and 7 are not used, and are always set to 0.
Bit 6 provides a means for you to determine if SRQ was asserted by the Model 6512. If this bit is
set, service was requested by the instrument. Bit 5 flags a Model 6512 error condition, which can
be further checked with the U1 command. If this bit is set, one of the following errors has occurred:
BIT
POSITION
VALUE
DECIMAL
WEIGHTING
1=RQS BY 6512
(STATUS BYTE ONLY)
1=ERROR
1=READY FOR NEW COMMAND
1=READING DONE
1=DATA STORE FULL
1=READING
OVERFLOW
B7 B6 B5 B4 B3 B2 B1 B0
0 1/0 1/0 1/0 1/0 0 1/0 1/0
128 64 32 16 8 4 2 1