2308-900-01 Rev. A / July 2008
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Section Topics
7-7
Model 2308 Portable Device Battery/Charger Simulator User’s Manual
Section 7: Status Structure
•
Bit B6, request service (RQS)/master summary status (MSS)
- Set bit indicates that an
enabled summary bit of the status byte register is set.
•
Bit B7, operation summary (OSB)
- Set summary bit indicates that an enabled operation
event has occurred.
Depending on how it is used, bit B6 of the status byte register is either the request for service
(RQS) bit or the master summary status (MSS) bit:
• When using the serial poll sequence of the power supply to obtain the status byte (a.k.a.
serial poll byte), B6 is the RQS bit (see
Serial polling and SRQ
).
• When using the
*STB?
command (see
Status byte and service request commands
) to read
the status byte, B6 is the MSS bit.
Service request enable register
The generation of a service request is controlled by the service request enable register. This
register is programmed by the user 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 7-2
, 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 (B6) 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 power is cycled or a parameter value of 0 is sent
with the
*SRE
command (i.e.
*SRE 0
). The commands to program and read the SRQ enable
register are listed in
Table 7-3
.
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 power supply. 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 MSS. The MSS bit stays set until all status byte summary bits are
reset.
SPE, SPD (serial polling)
The
SPE
,
SPD
general bus command is used to serial poll the power supply. 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.
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