SX8 User Manual
G-‐UM-‐00004 Rev 006
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Queues
Input Queue
The input queue in the switch is a first-‐in-‐first-‐out (FIFO) queue and is
256 characters in length. Data bytes received from the controller are
placed in the input queue in the order received. When a full message
unit is received, it is transferred to the parser.
If the input queue becomes full while the GPIB is being used, the data
acknowledge signal (DAQ) is not sent to the GPIB controller until a
character is transferred from the input buffer to the parser. This ensures
that no bytes in the program message are lost. However, the RS232C
interface has no DAQ signal and cannot be signaled when the input
queue becomes full. Therefore, characters sent to the SX8 switch are
lost.
If a new program message is received before the response to a query in
a previous message is read, the output queue is cleared, MAV is set to
false, and the query error bit is set. This error is also referred to as an
unterminated error.
Output Queue
Responses to query messages are placed in the output queue. This
queue is 256 characters in length. When a response is placed in the
output queue, the MAV bit in the status register is set. The MAV bit is
cleared when the response is sent.
Response messages are always terminated with the sequence <LF> and,
if the response is being sent through the GPIB, the EOI signal is set to
true when the last character in a response is sent.
If an attempt is made to read the output queue when it is empty and
the current program message does not contain a query, a query error
bit is set.
Error Queue
The error queue is where errors are placed and it can contain up to 10
error messages. Because it is a FIFO queue, the error returned when the
error queue is read is always the first error that occurred.
If more than 10 errors are put in the error queue, an overflow error
occurs and the last error in the queue is overwritten with error number
-‐350 (Queue Overflow). Each error in the queue consists of an error
number and a brief error message.
