Serial-S-Bus on RS422 issues

FAQ #100378

In principle, it is possible to use RS422 as physical layer for Serial-S-Bus communication. But note that the S-Bus full protocol is not fully applicatively due to the reason described below!


Configuring a serial port to use RS422
In order to switch the communication module (PCD7.F110, PCD3.F110, PCD7.F520 or PCD7.F530) from RS485 to RS422, the following code lines are to be used:


$INIT ; places following code into XOB 16 (Startup program block)
ACC L ; sets the ACCU to zero
SOCL portnr ; switches <portnr>, <portnr> is a value from 1 to 5
2 ; to RS422 mode
$ENDINIT ; end of code placed into XOB 16

As commented, this code is placed into the startup program block XOB 16 and will cause the port to work in RS422 mode. This means that it is only possible to use this port after the XOB 16 has been executed.
Please note that either the port is to be configured as PGU port or a SASI has been applied on <portnr> before executing the code above!
For further information, please refer to the S-Bus manual, 26/739.

Restriction for S-Bus full protocol
Given the situation that a program is to be downloaded to the PCD over such a port, we are faced with the following scenario:
Before downloading the code, PG5 will restart the PCD. This restart will reset all communication ports (and the concerned port will not be in RS422 mode any more). This leads to the fact, that PG5 won't get any response any more (and cannot send to the PCD, either). The PCD is to be restarted manually for establishing the communication again!
The same problem occurs after every restart command executed by PG5! This is why the RS422 is not really applicatively for real S-Bus full protocol actions. However, there is not problem in using all command except of the restart (and of course the S-Bus reduced protocol will not cause any problems).



PCD7 / Fxxx

PG5 2.0 / Serial-S-Bus

PCD3 / Fxxx

Last update: 20.05.2015 03:15

First release: 07.06.2005 08:44

Views: 3505

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