REXROTH IndraDrive Fc FCS01, Operating Instructions Manual

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15-46
Control Communication - Field Busses and Protocols Rexroth IndraDrive FCS01.1
DOK-INDRV*--FCS01*****-IB01_EN-P
Transmission Method
Only one slave device can be addressed with each telegram (exception:
broadcast telegram without slave response).
For reliable identification of the telegram start by the slave, the master
must observe a so-called
start break between the receipt of the slave
telegram and the transmission of the next telegram. The master starts
with transmitting a telegram. After transmission of the data package, the
master switches the bus data direction from send to transmit. Now, the
slave addressed in the telegram must respond within a specified
response delay time .
The telegram lengths of master and slave telegrams are always identical,
i.e. the master telegram defines the telegram length of the slave
response.
Telegram traffic can be cyclic or acyclic.
The following time definitions must be observed:
Time Size Significance
t
SB
Minimum 2 character runtimes:
Character runtime = 11 x (1/Baud
rate) Start - break time
t
CDT
Smallest start break time Character - delay time
t
RDT
Maximum 20 ms Response delay time
t
TRT
1.5 x flush telegram runtime
= 1.5 x (n+4) x character runtime
Max. telegram remaining
runtime
Fig. 15-61: Time definitions
Start - break time
The start character STX (= 02 Hex) on its own is not sufficient for the
slaves to reliably identify the start of a telegram because the bit
combination 02/Hex may also appear in the use characters. For this
reason, STX must be preceded by a character-less start-break character
t
SB
of at least 2 character runtimes for the master. The start-break time is
part of the job telegram. Only an STX with preceding start break
characterizes a valid telegram start.
Data exchange always proceeds in accordance with the schema
described above (semi-duplex operation).
See the 'master telegram times' tables for the minimum start-break
times which must be observed with the different Baud rates.
Response delay time
The time interval between the last character of the job telegram (BBC)
and the start of the response telegram (STX) is called
response delay
time t
RDT
. The maximum permissible response delay time is 20 ms but
must never be smaller than the start break . If the addressed node
does not respond within the maximum permissible response delay time,
an error message is stored in the master. Then, the master sends the
telegram intended for the next slave node.
See the 'master telegram times' tables for the smallest response delay
times which must be observed with the different Baud rates.