Remote Control System TT801 – User Guide
MU-TT801-AN rev.6 September 2009
51
III.9 Using the Serial Link
III.9.1 P
RINCIPLE
A serial link plug is present on the front panel of the TT801 cabinet. See section I.7 for the
description of the RS232/422 plug. This plug allows the operator to get access to data
measured by the TT801 unit (Range, Diagnostic Data, Pressure measurement,
Acknowledgement of Release execution…).
When the TT801 receives a signal from the Acoustic Release/Transponder, it displays the
results on its screen and simultaneously transmits strings containing the same results via
the serial link. The format of the strings is based on the NMEA 0183 standard.
III.9.2 S
ERIAL
L
INK
P
ARAMETERS
Each message is composed of a maximum of 79 ASCII printable characters ($20 to $7F)
with a front and rear character. This message is sent on the following format:
•
4800 bauds
•
1 start bit
•
8 bits without parity (MSB = 0)
•
1 stop bit
The following parameters have a significant meaning:
•
$
Message
start
•
, Fields
separator
•
*
Before the checksum
•
<CR><LF> Message
end
The checksum is computed by using a exclusive OR on the total set of bytes between the
$ and * characters without including these characters. The hexadecimal value of the
checksum byte is sent in a two characters format.
III.9.3 M
ESSAGE
S
TRUCTURE
A message is typically composed of the following structure:
$PMEVL,XP,RES,AAA,BBB,YP,CMD,xxxxxx *CK<CR><LF>
•
XP
Serial number of the TT801 remote control unit
•
RES
ID of the string (
RES
: Measure RESult …)
•
AAA
Type of Result data (See Table 7 for more details)
•
BBB
Type of interrogated beacon
•
YP
Serial number of the interrogated acoustic device,
IMM
if the
command is IMMediately sent without saving the configuration
•
CMD
Type of transmitted command (
IIF
,
CMD
ONLY
)
•
xxxxxx
Result depending of the type of transmitted data, error cases (no
answer from the beacon) are followed by the value ‘-1’
Depending of the command, the acoustic answer
AAA
can have different meanings.
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