Automating Manufacturing Systems - Process Control and ...

plc network - 28.13
1bit
11 bits
1bit
start of frame
identifier
ready to receive it
arbitration field
6 bits
0-8 bytes
15 bits
1bit
1bit
1bit
7 bits
>= 3 bits
control field - contains number of data bytes
data - the information to be passed
CRC sequence
CRC delimiter
ACK slot - other listeners turn this on to indicate frame received
ACK delimiter
end of frame
delay before next frame
Figure 28.10
A CANbus Data Frame
Because of the bitwise arbitration, the address with the lowest identifier will get
the highest priority, and be able to send messages faster when there is a conflict. As a
result the controller is normally put at address 0. And, lower priority devices are put near
the end of the address range.
28.2.3 Controlnet
Controlnet is complimentary to Devicenet. It is also supported by a consortium of
companies, (http://www.controlnet.org) and it conducts some projects in cooperation with
the Devicenet group. The standard is designed for communication between controllers,
and permits more complex messages than Devicenet. It is not suitable for communication
with individual sensors and actuators, or with devices off the factory floor.
Controlnet is more complicated method than Devicenet. Some of the key features