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What is the protocol sequence in the BIS L Easy Loop function?

Protocol sequence in BIS L Easy Loop function

Easy Loop connection system with a connected processor (individual telegram):


Fig.: Communication module with one processor



Data carrier data: 01hex 23hex 45hex 67hex 89hex

Query the system with control character <DLE>


<STX> <CR> '0' '1' '2' '3' '4' '5' '6' '7' '8' '9' 'SB' <ETX> '0' '0' <SP> 'BCC' 'BCC' <DLE>

20 characters are sent in the individual telegram:

1st character Start of Text (<STX>)

2nd character Line Break (<CR>)

3 rd–12th character Data carrier data

13th character Status byte ('SB')

14th character End of Text (<ETX>)

15th–17th character 00 (placeholder)

18th–19th character Block Check Character (BCC)

20th character Read command <DLE>)


Easy Loop connection system with two processors (data chain made up of two telegrams):

Fig. Communications module with two processors


Data chain:

Data carrier data 1: 01hex 23hex 45hex 67hex 89hex

Data carrier data 2: ABhex ABhex ABhex ABhex ABhex

Query the system with control character <DLE>


<STX> <CR> '0' '1' '2' '3' '4' '5' '6' '7' '8' '9' 'SB' <ETX> '0' '0' <SP>

<STX> <CR> 'A' 'B' 'A' 'B' 'A' 'B' 'A' 'B' 'A' 'B' 'SB' <ETX> '0' '0' <SP> 'BCC' 'BCC' <DLE>



The processors string the individual telegrams together into a data chain. Which of the telegrams are current can be read from the status byte ('SB') (CT-Present bit see “Status byte”.

At the end of the data chain is a calculated BCC, consisting of two ASCII characters.

This BCC is used to check for correct transmission of the telegrams.

The data chain is terminated with the control character <DLE>. This control character is used to start reading. When the control character <DLE> is received by the host system, reading of all processors is finished and all individual telegrams have been received. The telegrams can be processed and a new read command can be issued.



The next read command cannot be started until all processors have been read and

the host system has received the control character <DLE>. Errors may occur if new

read takes place too soon.


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