Message Queues; How The Input Queue Works; Clearing The Input Queue; The Output Queue - Keysight N774 C Series Programming Manual

1 Introduction to Programming

Message Queues

How the Input Queue Works

Clearing the Input Queue

The Output Queue

The Error Queue

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The instrument exchanges messages using an input and an output queue.
Error messages are kept in a separate error queue.
The input queue is a FIFO queue (first-in first-out). Incoming bytes are
stored in the input queue. The parser starts if the LF character is received.
Switching the power off, or sending a Device Interface Clear signal, causes
commands that are in the input queue, but have not been executed to be
lost.
The output queue contains responses to query messages. The instrument
transmits any data from the output queue when a controller addresses the
instrument as a talker.
Each response message ends with a LF (hex 0A). If no query is received, or
if the query has an error, the output queue remains empty.
The Message Available bit (MAV, bit 4) is set in the Status Byte register
whenever there is data in the output queue.
The error queue is 30 errors long. It is a FIFO queue (first-in first-out). That
is, the first error read is the oldest error to have occurred. For example:
1 If no error has occurred, the error queue contains:
o error"
+ 0, "N
2 After a command such as
o error"
+ 0, "N
-113, "Undefined header"
3 If the command is immediately repeated, the error queue now
contains:
o error"
+ 0, "N
-113, "Undefined header"
-113, "Undefined header"
Keysight N774xC Series Multiport Power Meter Programming Guide
wav:pow
, the error queue now contains: