Product Manual

7526A
Users Manual
5-14
1. Serial Poll Status Byte (STB)
The Calibrator sends the serial poll status byte (STB) when it answers to a serial poll.
This byte is set to 0 when the power is turned on. The STB byte structure is shown in
Table 5-7. Refer to the *STB? command in Chapter 6 for more information on how
to read this register.
Table 5-7. Serial Poll Status Byte (STB) and Service Request Enable (SRE) Registers
7 6 5 4 3 2 1 0
0
RQS
ESB MAV EAV 0 0 0
MSS
RQS Requesting Service. The RQS bit is set to 1 when bits ESB, MAV, EAV, or ISCB change from 0
to 1 and are enabled (1) in the SRE. When RQS is 1, the Product asserts the SRQ control line
on the IEEE-488 interface. You can do a serial poll to read this bit to see if the Product is the
source of an SRQ.
MSS Master Summary Status. Set to 1 when bits ESB, MAV, EAV, or ISCB are 1 and enabled (1) in
the SRE. This bit can be read with the *STB? Remote command in in place of a serial poll. Set to
1 when one or more ESR bits are 1.
MAV Message Available. The MAV bit is set to 1 when data is available in the IEEE-488 interface
output buffer of the Product.
EAV Error Available. An error has occurred and an error is available to be read from the error queue
with the FAULT? query.
2. Service Request (SRQ) Line
IEEE-488 Service Request (SRQ) is an IEEE-488.1 bus control line that the Product
asserts to tell the controller that some type of service is necessary. Many instruments
can be on the bus, but they all share one 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 Product was the source of the SRQ.
The Product 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 and
MAV are 0, or they are disabled when their related enable bits in the SRE register are
set to 0.
3. 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 Table 5-8 for the bit
functions.
4. Programming the STB and SRE
When you reset (to 0) the bits in the SRE, you can mask (disable) related bits in the
serial poll status byte. Bits set to 1 enable the related bit in the serial poll status byte.