User manual

2400 Series SourceMeter
®
User’s Manual Status Structure 15-9
Service request enable register
The generation of a service request is controlled by the Service Request Enable
Register. This register is programmed by you 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 15-3, the sum-
mary bits are logically ANDed (&) with the corresponding enable bits of the Ser-
vice 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. To read the Service Request Enable Reg-
ister, 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 com-
mand (i.e. *SRE 0). The commands to program and read the SRQ Enable Regis-
ter are listed in Table 15-3.
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 Sta-
tus 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 ser-
vice the request.
Typically, SRQs are managed by the serial poll sequence of the SourceMeter. 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 per-
formed. 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 sequence is used to serial poll the
SourceMeter. 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.