B&K Precision MDL Series - Programming Manual User Manual

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When data is placed in the output queue, the Message Available (MAV) bit in the Status Byte Register

gets set. A data message is cleared from the output queue when it is read. The output queue is

considered cleared when it is empty. An empty output queue clears the MAV bit in the Status Byte

Error queue

The error queue holds error and status messages. When an error or status event occurs, a message

that defines the error/status is placed in the error queue. This queue will hold up to 10 messages.

When a message is placed in the error queue, the Error Available (EAV) bit in the Status Byte Register is

set. An error message is cleared from the Error/Status queue when it is read. The error queue is

considered cleared when it is empty. An empty error queue clears the EAV bit in the Status Byte

:SYSTem:ERRor?

Status Byte and Service Request (SRQ)

Service request is controlled by two 8-bit registers: the Status Byte Register and the Service Request

Enable Register.

Status Byte Register

The summary messages from the status registers and queues are used to set or clear the appropriate

bits (B0, B2, B3, B4, B5, and B7) of the Status Byte Register. These bits do not latch, and their states (0

or 1) are solely dependent on the summary messages (0 or 1). For example, if the Standard Event

Status Register is read, its register will clear. As a result, its summary message will reset to 0, which in

turn will clear the ESB bit in the Status Byte Register.

Bit B6 in the Status Byte Register is either:

•

The Master Summary Status (MSS) bit, sent in response to the *STB? Command, indicates the

status of any set bits with corresponding enable bits set.

•

The Request for Service (RQS) bit, sent in response to a serial poll, indicates which device was

requesting service by pulling on the SRQ line.

For a description of the other bits in the Status Byte Register, see “Common commands, *STB?” The

IEEE-488.2 standard uses the following common query command to read the Status Byte Register:

*STB?

When reading the Status Byte Register using the *STB? command, bit B6 is called the MSS bit. None of

the bits in the Status Byte Register are cleared when using the *STB? command to read it.

The IEEE-488.1 standard has a serial poll sequence that also reads the Status Byte Register and is better

suited to detect a service request (SRQ). When using the serial poll, bit B6 is called the RQS bit. Serial