User manual

Section 12: Status Model Series 3700 System Switch/Multimeter Reference Manual

12-14 3700S-901-01 Rev. C / July 2008

Serial polling and SRQ

Any enabled event summary bit that goes from 0 to 1 sets bit B6 and generates

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.

SRQs can be managed by the serial poll sequence of the Series 3700. 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.

For common and script commands, B6 is the MSS (message summary status)

bit. The serial poll does not clear MSS. The MSS bit stays set until all status byte

summary bits are reset.

Service request enable register

The generation of a service request is controlled by the Service Request Enable

bit B6 (RQS/MSS) by the status summary message bits (B0, B2, B3, B4, B5,

and B7) of the status byte register. The summary bits are logically ANDed (&)

with the corresponding enable bits of the service request enable register. When

a set (1) summary bit is ANDed 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 or its script equivalent. To read the service request enable register,

use the *SRE? query or script equivalent. The service request enable register

clears when power is cycled or a parameter value of 0 is sent with the *SRE

command (for example, *SRE 0).

SPE, SPD (serial polling)

For the GPIB interface only, the SPE and SPD general bus command sequence

is used to serial poll the Series 3700. 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.