HP 8920A, User Manual

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S:\HP892XX\USRGUIDE\manual\encoscrn.fb
Chapter 10, Signaling Encoder (AF Generator 2)
MPT 1327 Encoder
The IBASIC test program occasionally alters the content of the forward control
channel temporarily (for example to send an ACKI in response to an RQS). The
message buffer enables IBASIC to do this without having to reload the filler
buffer.
The control channel message buffer (like the filler buffer), comprises 32 locations,
corresponding to the 32 timeslot capacity of the filler buffer. These are accessed
through HP-IB with the following command:
ENCoder:MPT1327:MESSage:CONTrol:DATA n,string
Where
• n is the location selector and has the range 1 through 32.
• string is a string containing a signaling command. The signaling command is assembled
as for the filler buffer and written into the selected location. If the signaling command
has one of the data codeword extensions (DCW2 or DCW4), subsequent timeslot loca-
tions are overwritten with the data codewords.
The control channel message buffer is activated by the following HP-IB
command:
ENCoder:SEND
If the encoder is configured for single operation, the message buffer contents will
be sent once.
If the encoder is configured for burst or continuous operation, the control channel
message buffer can be de-activated by the following HP-IB command:
ENCoder:STOP
The ENC:STOP/ENC:SEND command sequence is also an UPDATE command.
New timeslot contents written using ENC:MPT1327:MESS:CONT:DATA are
buffered until the STOP/SEND sequence causes the control message buffer to be
updated.
NOTE: The encoder’s sending status can be monitored to establish when a message has been sent by
looking at the bit-8 “Encoder sending Aux Information” in the Hardware Status Register #1.
For further information on the Hardware Status Register refer to the Programmer’s Guide.
When the
Test Mode
field is in
Control
mode and the control message buffer is
activated by ENC:SEND, the signaling firmware/hardware cycles through the
defined part of the filler buffer. It transmits each 128-bit filler buffer timeslot in
turn. This happens except where there is a message defined in the corresponding
timeslot of the control message buffer. In this case the contents of the control
message buffer are transmitted as shown in
figure 103 on page 413
.