Fluke 5502A - Service Request (SRQ) Line; Service Request Enable Register (SRE)

5502A
Operators Manual
5-40
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0
RQS
MSS
ESB MAV EAV ISCB 0 0
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 5502A
asserts the SRQ control line on the IEEE-488 interface. You can do a serial poll to read
this bit to see if the 5502A is the source of an SRQ.
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.
Set to 1 when one or more enabled ESR bits are 1.
Message available. The MAV bit is set to 1 when data is available in the IEEE-488
interface output buffer of the 5502A.
Error available. An error has occurred and an error is available to be read from the
error queue by using the ERR? query.
One or more enabled ISCR bits are 1.
RQS
MSS
ESB
MAV
EAV
ISCB
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Figure 5-9. Serial Poll Status Byte (STB) and Service Request Enable (SRE)
Service Request (SRQ) Line
IEEE-488 Service Request (SRQ) is an IEEE-488.1 bus control line that the Calibrator
asserts to tell the controller that some type of service is necessary. Many instruments can
be on the bus, but they all share a single SRQ line. To find which instrument set SRQ, the
Controller typically does a serial poll of each instrument. The calibrator asserts SRQ
when the RQS bit in its Serial Poll Status Byte is 1. This bit tells the controller that the
Calibrator was the source of the SRQ.
RS-232 Remote operations with the RS-232 interface emulate the IEEE-488 SRQ line
with an SRQSTR string sent with the serial interface when the SRQ line is set. (See the
SRQSTR command description in Chapter 6 for more information.)
The Calibrator clears SRQ and RQS when the controller/host does a serial poll, sends
*CLS, or when 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.
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.