HP 8920A, User Manual

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S:\HP892XX\USRGUIDE\manual\decoscrn.fb
Chapter 8, Signaling Decoder Screen
MPT 1327 Decoder
Detecting and Querying Messages
IBASIC can be informed about the arrival of a message in the decoder buffer. To
do this, configure the HP-IB status registers to cause a service request (SRQ) on
the negative transition event of bit 12, “Decoder Result Available” in the
Hardware Status Register #1.
For further information on the Hardware Status Register refer to the
Programmer’s Guide.
The message is read from the decoder buffer by the command:
MEASure:DECoder:MPT1327:BUFFer?
This query returns a quoted string comprising the contents of one or more
timeslots. The string is disassembled into mnemonic form. If more than one
message is received, the individual messages are separated by semicolons. If a
timeslot contains data codewords, it is disassembled into the DCW extension.
Examples of this are:
• Simple RQS from RU. RQS 0,1,5,0
• Cleardown from RU sent in three consecutive timeslots.
MAINT 0,1,283,3,0;MAINT 0,1,283,3,0;MAINT 0,1,283,3,0
• SAMIS response to AHYC giving PSTN digits for call.
SAMIS 14391,83782;DCW #H080000000000,#H000000000000
There are two other measurements available on the decoder screen:
• The Signaling Data Rate. The signaling data rate measurement is the measured baud
rate of the received message. It is most accurately measured on a “dotting” pattern.
• The Received Message Timing. This measures the timing of the received message rel-
ative to the timeslots in the forward control channel. It has two modes of operation:
•Slot timing mode. This works in the
Control
test mode only, it is disabled in
all other modes. This is the default mode.
•The timing counter is reset at the end of every control channel timeslot. If a mes-
sage is received, the time from the most recent slot end, to the start of the received
message’s preamble, is reported as the timing measurement result.