W&T Com-Server++, Manual

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85
W&T
Packetizing serial datagrams
Subject to error and alteration
n
Byte Order
Organization of the length field (net order = high-byte-
first; byte order = low-byte-first)
n
Additional Bytes
Any number of bytes which may not be accounted for in
the length specification of the serial protocol (e.g.
Start
Sequence , appended checksum, etc.). This means the con-
tents of the field defined by Size may have to be corrected
to the total length of the serial datagram using the Addi-
tional Bytes option.
Example
The serial protocol shown in the following always starts with
the character
STX (0x02). In the Length field the length of
the following data field (serial data) is specified without the
checksum and without the previous fields. The Block End is
indicated by a variable 16-bit checksum.
Description
Size [byte]
Value
Start
Sequence
Serial
Address
Len-Field
(Netorder)
Serial
Data
CRC16
1
STX (02) any High/Low
1 2 x 2
any
=
The following settings must be made on the Comt-Server for
correct packeting of this protocol structure:
As soon as the Com-Server has received the character 0x02 it
collects additional data. If the total number of incoming cha-