Agilent Technologies E1300B, E1301B Reading the Status Byte Register, Bit Decimal Number

Reading the Status Byte Register

Table 4-1 shows each of the Status Byte register bits and describes the event that will set each bit.

		Table 4-1. Status Byte Register
Bit	Decimal
Number	Weight	Description
0	1	Instrument Specific (not used by most instruments)
1	2	Instrument Specific (not used by most instruments)
2	4	Instrument Specific (not used by most instruments)
3	8	Questionable Data Status Group Summary Bit. One or more events
		in the Questionable Data Status group have occurred and set
		bit(s) in those registers.
4	16	Message Available. The instrument’s output queue contains
		information. This bit can be used to synchronize data exchange
		with an external computer. For example, you can send a query
		command to the instrument and then wait for this bit to be set.
		The GPIB is then available for other use while the program is
		waiting for the instrument to respond.
5	32	Standard Event Status Group Summary Bit. One or more enabled
		events in the Standard Event Status Register have occurred and
		set bit(s) in that register.
6	64	Service Request--Service is requested by the instrument and the
		GPIB SRQ line is set true. This bit will be set when any other bit
		of the Status Byte Register is set and has been enable to assert
		SRQ by the *SRE command.
7	128	Operation Status Group Summary Bit. One or more events in the
		Operation Status Group have occurred and set bit(s) in those
		registers.

You can read the Status Byte register using either the *STB? command or an GPIB serial poll. Both methods return the decimal weighted sum of all set bits in the register. The difference between the two methods is that *STB? does not clear bit 6 (Service Request); serial poll does clear bit 6. No other status register bits are cleared by either method with the exception of the Message Available bit (bit 4) which may be cleared as a result of reading the response to *STB?. In addition, using an GPIB serial poll lets you read the status byte without interrupting the instrument parser. The *STB? method requires the instrument to process the command. This can generate interrupt query errors if the instrument is executing another query.

The following program uses the *STB? command to read the contents of the system instrument’s (Command Module’s) Status Byte register.

10 OUTPUT 70900;"*STB?"	Read Status Byte Register
20 ENTER 70900; A	Enter weighted sum
30 PRINT A	Print weighted sum
40 END

For example, assume bit 3 (weight = 8) and bit 7 (weight = 128) are set. The above program returns the sum of the two weights (136).

6-4 Controlling Instruments Using GPIB