Fluke 5500A - Service Request (SRQ) Line; Service Request Enable Register (SRE)

Remote Operation
Checking 5500A Status 5
5-37
76543210
0
RQS
MSS
ESB MAV EAV ISCB 0 0
RQS Requesting service. The RQS bit is set to 1 whenever bits ESB, MAV, EAV, or ISCB change from 0
to 1 and are enabled (1) in the SRE. When RQS is 1, the 5500A asserts the SRQ control line on
the IEEE-488 interface. You can do a serial poll to read this bit to see if the 5500A is the source of
an SRQ.
MSS Master summary status. Set to 1 whenever bits ESB, MAV, EAV, or ISCB are 1 and enabled (1) in
the SRE. This bit can be read using the *STB? command in serial remote control in place of doing
a serial poll.
ESB Set to 1 when one or more enabled ESR bits are 1.
MAV Message available. The MAV bit is set to 1 whenever data is available in the 5500A’s IEEE-488
interface output buffer.
EAV Error available. An error has occurred and an error is available to be read from the error queue by
using the ERR? query.
ISCB One or more enabled ISCR bits are 1.
F5-05.eps
Figure 5-9. Serial Poll Status Byte (STB) and Service Request Enable (SRE)
5-44. Service Request (SRQ) Line
IEEE-488 Service Request (SRQ) is an IEEE-488.1 bus control line that the 5500A
Calibrator asserts to notify the controller that it requires some type of service. Many
instruments can be on the bus, but they all share a single SRQ line. To determine which
instrument set SRQ, the Controller normally does a serial poll of each instrument. The
calibrator asserts SRQ whenever the RQS bit in its Serial Poll Status Byte is 1. This bit
informs the controller that the calibrator was the source of the SRQ.
RS-232 Remote operations using the RS-232 interface emulate the IEEE-488 SRQ line
by sending the SRQSTR string over the serial interface when the SRQ line is set. (See
the SRQSTR command description in Chapter 6 for more information.)
The 5500A Calibrator clears SRQ and RQS whenever the controller/host performs a
serial poll, sends *CLS, or whenever the MSS bit is cleared. The MSS bit is cleared only
when ESB, MAV, EAV, and ISCB are 0, or they are disabled by their associated enable
bits in the SRE register being set to 0.
5-45. Service Request Enable Register (SRE)
The Service Request Enable Register (SRE) enables or masks the bits of the Serial Poll
Status Byte. The SRE is cleared at power up. Refer to Figure 5-9 for the bit functions.