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SATEL OY
// SATELLAR MANUAL // RADIO UNIT // USER GUIDE // V. 1.8
6. Data transmission
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6.6.3 Error control
For error checking purposes there is a mechanisms in the RU: cyclic redundancy check (CRC).
Cyclic redundancy check
is possible for the user to switch ON, Partial and OFF. When CRC = ON the trans-
mitter calculates the checksum based on the whole data stream, which has been received. If the check
is ok, the data is sent to UART. A drawback in this is that the latency increases by the transfer time of the
whole packet. In some applications it may be useful to use CRC=Partial, in this case transmitter is working
on block-by-block basis so that once a block of data is checked to be ok, it is transmitted immediately
and then next data block is checked. With CRC=Partial there’s a possibility of latter blocks be wrong in
which case the transfer is stopped (but all so far transferred data is still correct). If CRC Check is OFF, data
transfer is stopped once CRC is noticed to be wrong but there may have been erroneous data sent to UART
before this.
The basic guidelines how to use the error control features are the following:
–
When it is important to be sure that the data is correct but the latency is not critical:
switch the CRC ON.
–
When every received character being correct it is not critical and the latency is
critical: switch the CRC OFF.
6.6.4 Pause length
Pauses are used to separate two messages from each other at the serial interface. A typical pause length,
which is interpreted, as the end of the message is three characters. However, non-real time operating sys-
tems used in many DTE easily add random pauses in the data stream. Those pauses are then seen as mes-
sage breaking points in the RU. To overcome this situation pause length parameter has been introduced
and must be set higher than the worst-case pause in the data stream. The data stream from the DTE must
then take this setting into account: the RU does not recognize the pauses that are shorter than the value of
the pause length parameter.
