Stanford Research Systems SR865A, Руководство по эксплуатации

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Chapter 4 Programming 151
SR865A DSP Lock-in Amplifier
Status Byte Definitions
The SR865A reports on its status by means of four status bytes: the Serial Poll Status
byte, the Standard Event Status byte, the LIA Status byte, and the Error Status byte.
The status bits are set to 1 when the event or state described in the tables below has
occurred or is present.
Serial Poll Status Byte
bit name usage
0 unused
1 unused
2 ERR An enabled bit in the error status byte has been set.
3 LIA An enabled bit in the LIA status byte has been set.
4 MAV The interface output buffer is non-empty.
5 ESB An enabled bit in the standard status byte has been set.
6 SRQ SRQ (service request) has occurred.
7 unused
The ERR, LIA, and ESB bits are set whenever any bit in BOTH their respective status
bytes AND enable registers is set. Use the
SRE , ESE , ERRE and LIAE commands to
set enable register bits. The ERR, LIA and ESB bits are not cleared until ALL enabled
status bits in the Error, LIA and Standard Event status bytes are cleared (by reading the
status bytes, using
CLS or by clearing the enable register bits).
Using STB? command to read the Serial Poll Status Byte
A bit in the Serial Poll status byte is NOT cleared by reading the status byte using
*
STB? .
The bit stays set as long as the status condition exists. This is true even for SRQ. SRQ
will be set whenever the same bit in the serial poll status byte AND enable register is set.
This is independent of whether a serial poll has occurred to clear the service request.
Using GPIB Serial Poll
Except for SRQ, a bit in the Serial Poll status byte is NOT cleared by GPIB serial polling
the status byte. When reading the status byte using a GPIB serial poll, the SRQ bit signals
that the SR865A is requesting service. The SRQ bit will be set (1) the first time the
SR865A is polled following a service request. The GPIB serial poll automatically clears
the service request SRQ. Subsequent GPIB serial polls will return SRQ cleared (0) until
another service request occurs.
Polling the status byte and reading it with
*
STB? can return different values for SRQ.
When polled, SRQ indicates a service request has occurred. When read, SRQ indicates
that an enabled status bit is set.
GPIB Service Requests (SRQ)
A GPIB service request (SRQ) will be generated whenever a bit in both the Serial Poll
Status byte AND Serial Poll Enable register is set. Use
*
SRE to set bits in the Serial Poll
Enable register. A service request is only generated when an enabled Serial Poll Status bit
becomes set (changes from 0 to 1). An enabled status bit which becomes set and remains