Bus Transmission - ABB 07CR41 Operating Manual

1.3.3

Bus transmission

3
The master basic unit manages the transmission of messages to the various slaves via the
RS485 connection.
The messages are transmitted in the following format:
- Request from the master basic unit:
address
- Request from the remote units:
start
The messages always end with an end of frame control character: checksum CRC8.
The length of the exchanged frames depends on the type of unit. Frames exchanged with
analog units are the longest.
The basic unit interrogates the remote units to establish an initial image of the system configu-
ration during initialization.
The remote units are then interrogated with each bus cycle. This enables the recognition of
newly added or removed remote units and the update of the diagnosis information.
If the basic unit receives a message indicating a CRC8 error, it will not be signaled immedi-
ately and the frame will not be taken into account. After nine consecutive transmission errors,
a "bus error" is signaled by the basic unit. The bus error is also signaled to the remote units
after a 250 ms time-out.
Introduction
data CRC8
data CRC8
1 – 6
Advant Controller AC 31 / Issued: 01.99