Instruction manual

The Status Byte Register

The status byte summary register reports conditions from other status

registers.Query data that is waiting in the instrument’s output buffer is immediately reported

through the “message available” bit (bit 4). Bits in the summary registers are not latched.

Clearing an event register will clear the corresponding bits in the status byte summary

the message available bit.

BIT DEFINITIONS-STATUS BYTE REGISTER

BIT DESCRIPTION DECIMAL

VALUE DEFINITION

0 Not Used 1 Always set to 0.

1 Not Used 2 Always set to 0.

2 Questionable Data 4 One or more bits are set in the Questionable

Data register (bits must be “enabled” in enable

3 Not Used 8 Always set to 0.

4 Message Available 16 Data is available in the Instrument’s output

buffer.

5 Standard Event 32 One or more bits are Set in the Standard Event

6 Request Service 64 The Instrument is requesting the SERVICE

(Serial Poll).

7 Not Used 128 Always set to 0.

The Status byte summary register is cleared when:

♦ You execute a * CLS (clear status) command.

♦ Querying the standard event and questionable data registers will clear only the respective

bits in the summary register.

The status byte enable register (request service) is cleared when:

* You turn on the power to the instrument.

* You execute a *SRE 0 command.

USING *STB? TO READ THE STATUS BYTE

The *STB? (Status byte query) command is similar to a serial poll except it is pro-

cessed like any other instrument command. The *STB? Command returns the same result

as an IEEE-488 serial poll except that the “request service” bit (bit 6) is not cleared if a serial

poll has occurred. The *STB? Command is not handled automatically by the IEEE-488 bus

interface hardware and the command will be executed only after previous commands have

completed. Polling is not possible using the *STB? Command. Using the *STB? Command

does not clear the status byte summary register.