PK-232 MBX Operating Manual - N3UJJ

PK-232 OPERATING MANUAL
COMMAND SUMMARY
SAmple “n”
Mode: Command
Immediate Command
Host: SA
“n" — 20 to 255 specifies the sampling rate in baud.
This is a new operating mode with the Summer 1991 PK-232 firmware release for
advanced users interested in decoding unknown synchronous data transmissions.
SAMPLE is similar to the SBIT and 6BIT modes, but operates on synchronous data,
whereas 5B1T and 6BIT are used on signals known to be asynchronous.
SAMPLE syncs up on any regularly-paced data transmission and samples the data
once per bit, packaging the data in groups and sending the groups to the user for
further analysis. The user can use SAMPLE to capture data bits from a
synchronous transmission, such as FEC, TDM or an 'unknown model' not identified
by the SIGNAL command. The transmission is actually sampled several times per
data bit. The PK-232 does a majority vote an the last few samples to represent
the value of the data bit.
One use for the SAMPLE command is to record the output to a disk file, then write
a program to analyze the results for synchronous/asynchronous, bit sync patterns,
data decoding, etc.
SAMPLE data is captured in 6-bit units; the order of bit reception is MSB first,
LSB last. The TNC sends the data unit to the user with a constant of hex 30
added to each unit, the same as the 6BIT command. The 6-bit unit is a compromise
between hexadecimal and 8-bit binary output, The 6-bit unit yields shorter disk
files than 4-bit hexadecimal characters, but encounters no interference from
terminal communications programs and the TNC's Converse and Command modes. The
6-bit unit's range of $30-6F falls within the printable ASCII range, allowing the
TNC to insert end-of-line carriage returns that can be ignored by the user's
analysis software.
To use SAMPLE, set ACRDISP to a non-zero value such as 77. This will break up
the recorded disk file into lines. Tune in the signal, set WIDESHFT ON or OFF as
needed, and get the transmission rate from the SIGNAL command. Now type "SAMPLE
(rate)". As an example, SIGNAL may identify a transmission as 96 baud TDM; in
this case type the following:
SAMPLE 96
Now begin the capture to a disk file with the terminal program. At the end of the
session, edit the disk file and remove any TNC commands that were echoed before
or after the received data.
Occasionally SIGNAL will identify a Baudot transmission at a rate that SAMPLE
cannot sync up on. This would happen if the Baudot signal had a stop bit
duration 1.5 times the data bit duration. In this case, SAMPLE at twice the baud
rate and compensate for the doubled data bits in the analysis software. Note that
it might be more useful to let the TNC do the start/stop bit work by using the
5BIT command rather than SAMPLE. 5BIT uses RBAUD, and adds a constant of hex 40
to each 5-bit character received.
Note:
RXREV does affect the sense of the SAMPLE data.
RXREV should however not be changed while capturing data.
8/91 A-69
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