Anritsu MS8608A, Operation Manual, Page: 237 / 338

SECTION 4 STATUS STRUCTURE
4-5
Status Byte (STB) Register
The STB register consists of the STB and RQS (or MSS) messages of the device.
ESB and MAV summary messages
This paragraph describes the ESB and MAV summary messages.
(1) ESB summary message
The ESB (Event Summary Bit) is a message defined by IEEE488.2 which uses bit 5 of the
STB register. When the setting permits events to occur, the ESB summary message bit
becomes 1 if any one of the events recorded in the Standard Status Register becomes 1.
Conversely, the ESB summary message bit becomes 0 if one of the recorded events occurs,
even if events are set to occur.
This bit becomes 0 when the ESR register is read by the
∗
ESR? query or when it is
cleared by the
∗
CLS command.
(2) MAV summary message
The MAV (Message Available) summary bit is a message defined by IEEE488.2 which
uses bit 4 of the STB register. This bit indicates whether the output queue is empty.
The MAV summary message bit is set to 1 when a device is ready to receive a request
for a response message from the controller. When the output queue is empty, this bit is
set to 0. This message is used to synchronize the information exchange with the
controller. For example, this message is available when, after the controller sends a
query command to a device, the controller waits until MAV becomes 1. While the
controller is waiting for a response from the device, other jobs can be processed. Reading
the Output Queue without first checking MAV will cause all system bus operations to
be delayed until the device responds.