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The following program reads the system instrument’s Status Byte register using
the GPIB Serial Poll command.
10 P= SPOLL(70900) Read Status Byte Register using
Serial Poll, place weighted sum
in P
20 PRINT P Print weighted sum
30 END
Service Request
Enable Register
The Service Request Enable register is used to "unmask" bits in the Status Byte
register. When an unmasked Status Byte register bit is set to ’1’, a service
request is sent to the computer over GPIB.
The command used to unmask Status Byte register bits is:
*SRE < mask>
where < mask> is the decimal weight of the bit to be unmasked, or is the sum
of the decimal weights if multiple bits are to be unmasked. For example,
executing:
*SRE 16
unmasks the message available (MAV) bit in the Status Byte register. Sending:
*SRE 48
unmasks the message available (MAV) and event status bit (ESB).
You can determine which bits in the Status Byte register are unmasked by
sending the command:
*SRE?
This command returns the decimal weighted sum of all unmasked bits.
The Service
Request Bit
Note that the Service Request bit (bit 6) in the Status Byte register does not
have a mask. Bit 6 is set any time another Status Byte register bit is set. If the
other bit which is set is unmasked, a service request is generated.
Clearing the Service
Request Enable
Register
The Service Request Enable register mask is cleared (each bit masked except
bit 6) by sending the command:
*SRE 0
If *PSC 1 has been executed, the Service Request Enable register mask is
cleared when power is cycled. If *PSC 0 has been executed, the mask is
unchanged when power is cycled. (*PSC? queries the setting.)
Controlling Instruments Using GPIB 6-5