EXFO IQS-600 Integrated Qualification System - Manual (Page 184)

Using IQS Products in an Automated Test Environment
176 IQS-600
Message Management
Message Management
Each device that is physically connected to the GPIB link has its own input
buffer, output queue and error/event queue. These data structures allow
storage of incoming messages (single or compound commands that are
sent to an instrument), responses from queries, errors and events that may
occur.
Data structure Characteristics Clearing
Input buffer

Consists of a First-In, First-Out
(FIFO) data structure.

Stores Data Bytes (DABs) and END
messages.

Delivers messages to the parser in
the order that they were received
from the I/O control.

Maximum message length:
unlimited in DABs (the input buffer
size is only limited to the total size
of the device memory).

An incoming byte empties the
output queue. An error will be
raised if the output queue
contained data. Consequently, it
clears the Message AVailable bit
(bit number 4 –MAV from the
Status Byte register).
The buffer will be cleared
by:

Turning off the power.

Sending a Device Clear
(DCL) message to the
instrument.

Sending a
Selected Device Clear
(SDC) message to the
instrument.