Keithley 6482, Справочное руководство

Страница: 171 / 350

13-8 Return to Section Topics 6482-901-01 Rev. A / August 2012
Section 13: Status Structure Model 6482 Dual-Channel Picoammeter / Voltage Source Reference Manual
Service request enable register
The generation of a service request is controlled by the service request enable register. This
register is programmed by you and is used to enable or disable the setting of bit B6 (RQS/MSS) by
the status summary message bits (B0, B2, B3, B4, B5, and B7) of the status byte register. As
shown in
Figure 13-3 , a logical AND (&) operation is performed on the summary bits and the
corresponding enable bits of the service request enable register. When a set (1) summary bit has
a logical AND (&) operation performed with an enabled (1) bit of the enable register, the logic “1”
output is applied to the input of the OR gate and, therefore, sets the MSS/RQS bit in the status
byte register.
The individual bits of the service request enable register can be set or cleared by using the *SRE
common command. To read the service request enable register, use the *SRE? query command.
The service request enable register clears when the instrument is restarted or a when parameter
value of 0 is sent with the *SRE command (for example, *SRE 0). The commands to program and
read the service request enable register are listed in
Table 13-3 .
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 will set bit B6 and generate an SRQ (service
request). In your test program, you can periodically read the status byte to check if an SRQ has
occurred and what caused it. If an SRQ occurs, the program can, for example, branch to an
appropriate subroutine that will service the request.
Typically, SRQs are managed by the serial poll sequence of the Model 6482. If an SRQ does not
occur, bit B6 (RQS) of the status byte register will remain cleared, and the program will simply
proceed normally after the serial poll is performed. If an SRQ does occur, bit B6 of the status byte
register will set, and the program can branch to a service subroutine when the SRQ is detected by
the serial poll.
The serial poll automatically resets RQS of the status byte register. This allows subsequent serial
polls to monitor bit B6 for an SRQ occurrence generated by other event types. After a serial poll,
the same event can cause another SRQ, even if the event register that caused the first SRQ has
not been cleared.
The serial poll does not clear the master summary status bit (MSS). The MSS bit stays set until all
status byte summary bits are reset.
SPE, SPD (serial polling)
The SPE, SPD general bus command sequence is used to serial poll the Model 6482. Serial
polling obtains the serial poll byte (status byte). Typically, serial polling is used by the controller to
determine which of several instruments has requested service with the SRQ line.
Status byte and service request commands
The commands to program and read the status byte register and service request enable register
are listed in
Table 13-3 . For details on programming and reading registers, see “Programming
enable registers,” page Section 13-4 , and “Reading registers,” page Section 13-5 .
NOTE To reset the bits of the service request enable register to 0, use 0 as the parameter value
for the *SRE command (for example, *SRE 0).