AP29002
Standalone TwinCAN Controller
Using special features of the 82C900
Application Note
53
V 1.0, 2004-02
3.11
Using the FIFO-buffering in a gateway application
If two CAN-Busses with different speeds are connected via the gateway function a
data loss can easily occur when the source-object of the gateway receives the
messages faster than the destination-object can transmit them on the slower CAN-
Bus. The 82C900 provides a solution for this problem, using a FIFO-Buffer as a
destination-object. The FIFO-Buffer must be configured in the same way as the
transmitting Buffer in the last example. The source-object is pretty similar to the
source-object of a Normal-Gateway except that FISIZE is not zero but equal FSIZE of
the destination-buffer and CANPTR must be initialized with the object-number of the
base object of the destination-buffer.
The following example configures message object zero as the source object
connected to node A at 1 MBaud, and a FIFO of 8 message objects as destination
object connected to node B at 125 KBaud. The FIFO-Buffer is configured as a
transmitting buffer with message object 16 as base object. The ID and the data length
code is copied from the source side to the destination side.
Figure 14
Normal Gateway with FIFO-Buffer
C A N - B U S 1 1 M B a u d
C A N - B U S 2 1 2 5 K B a u d
N o d e A
M e s s a g e o b j e c t0 I D 1 , R e c e i v in g
O b j e c t, N o r m a l G a t e w a y , 4 D a t a b y t e ,
a u to m a t ic t r a n s m i t ti o n o n s o u r c e s i te
F IF O -B u f fe r I D c o p i e d , B a s e o b j e c t 1 6
tr a n s m i tt i n g b u f fe r , 8 M e s s a g e o b j e c t s
D a t a b y t e n u m b e r c o p i e d
N o d e B
