AP29002
Standalone TwinCAN Controller
Using special features of the 82C900
Application Note
29
V 1.0, 2004-02
3.3
Hardware Gateway functionality
The 82C900 also provides the possibility to act as a gateway between two CAN-
Busses. It doesn’t matter if the CAN-Busses work at the same speed. So it can be
used to connect a High- and a Low-speed CAN Bus with or without any control of a
microcontroller. The Gateway function has two modes. The first mode is the Normal
Gateway Mode. This mode provides the possibility to send messages from e.g. Node
A to Node B and at the same time it can forward remote frames from Node B to Node
A. But it needs two message objects for each direction.
The second mode is the Shared-Gateway-Mode. This mode only needs one message
object per direction.
But it can only receive messages/remote frames from one Node at a time. So it can
happen, that a message on CAN-Bus A gets lost without any detection, during the time
the gateway waits for a remote frame on CAN-Bus B.
3.4
Normal Gateway Mode
The following section describes how to connect two CAN-Busses operating with
different speeds. CAN-Bus 1 with a speed of 1 Mbaud will be connected to Node A
and CAN-Bus 2 with a speed of 125 Kbaud will be connected to Node B. The SSC-
Interface will be used for the configuration.
In this application two messages objects will be configured. MSGOB0 will be a
receiving object on node A and MSGOBJ1 will be a transmitting object on node B.
Both are additionally configured for the normal gateway mode. So all messages that
are received on node A with the ID 0x001 will be automatically transmitted on node B
with the same identifier. To configure a bi-directional gateway two more message
objects need to be configured with just switched nodes. The source files and the
project are in the “Normal_Gateway” directory.
