SRS Labs SR850 manual Remote Programming, Interface Ready and Status, GET Group Execute Trigger

Remote Programming

computer is ready to receive. If either buffer over- flows, both buffers are cleared and an error reported.

The present value of a particular parameter may be determined by querying the SR850 for its value. A query is formed by appending a question mark "?" to the command mnemonic and omitting the desired parameter from the command. Values returned by the SR850 are sent as a string of ASCII characters terminated by a carriage return <cr> on RS232 and by a line-feed <lf> on GPIB. If multiple queries are sent on one command line (separated by semicolons, of course) the answers will be returned individually, each with a terminator.

Examples of Command Formats

FMOD 0<lf>	Set reference source to
	internal
FREQ 10E3 <lf>	Set the internal reference fre-
	quency to 10000 Hz (10 kHz)
❊IDN? <lf>	Queries the device
	identification
STRT <lf>	Starts data acquisition (same
	as [START] key)
OUTP? 1 <lf>	Queries the value of X

INTERFACE READY AND STATUS

The Interface Ready bit (bit 1) in the Serial Poll Status Byte signals that the SR850 is ready to receive and execute a command. When a com- mand is received, this bit is cleared indicating that an operation is in progress. While the operation is in progress, no other commands will be pro- cessed. Commands received during this time are stored in the buffer to be processed later. Only GPIB serial polling will generate a response while a command is in progress. When the command execution terminates, the Interface Ready bit is set again and new commands will be processed. Since most commands execute very quickly, the host computer does not need to continually check the Interface Ready bit. Commands may be sent one after another and they will be processed immediately.

However, some commands, such as file com- mands and math operations, may require a long time to execute. In addition, the host program may need to check that these operations executed without error. In these cases, after the command is

sent, the Status Bytes should be queried.

When using the GPIB interface, serial polling may be used to check the Interface Ready bit in the Serial Poll Byte while an operation is in progress. After the Interface Ready bit becomes set, signal- ling the completion of the command, then the ERR or ESB bit may be checked to verify successful completion of the command.

If the RS232 interface is used, or serial polling is not available, then the ❊STB?, ❊ESR?, ERRS?, and LIAS? status query commands may be used to query the Status Bytes. Since the SR850 pro- cesses one command at a time, the status query will not be processed until the previous operation is finished. Thus a response to the status query in itself signals that the previous command is fin- ished. The query response may then be checked for various errors.

For example, the command line SDAT;ERRS? <lf> will save the data to disk and return the Error Status Byte when finished. The Disk Error bit (bit

3)may be checked to make sure that the Save Data (SDAT) command terminated without error. Since the Save Data command may take a long time to execute, it is important that the host com- puter interface does not time out while waiting for the response to the ERRS? query. In the case where the host interface times out before the ERRS? response, the host program must wait before sending the ERRS? query.

GET (GROUP EXECUTE TRIGGER)

The GPIB interface command GET is the same as the TRIG command. GET is the same as a trigger input. GET only has an effect if the sampling rate is triggered or if triggers start a scan.

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