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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
TwinCAN Module
User’s Manual
21-33
V2.2, 2004-01
TwinCAN_X1, V2.1
21.1.6.2
Normal Gateway with FIFO Buffering
MMC
<d>
= ‘01x’:
When the gateway destination object is programmed as FIFO buffer, bitfield CANPTR
<s>
is used as pointer to the FIFO element to be addressed as destination for the next copy
process. CANPTR
<s>
has to be initialized with the message object number of the FIFO
base element on the destination side. CANPTR
<s>
is automatically updated according to
the FIFO rules, when a data frame was copied to the indicated FIFO element on the
destination side. Bit GDFS
<s>
determines if the TXRQ
<d>
bit in the selected FIFO element
is set after reception of a data frame copied from the source side.
The base message object is indicated by <ba>, the slave message objects by <sl>. The
number of base and slave message objects, combined to a buffer on the destination
side, has to be a power of two (2, 4, 8 etc.) and the buffer base address has to be an
integer multiple of the buffer length. Bitfield CANPTR
<ba>
of the FIFO base element and
bitfield CANPTR
<s>
have to be initialized with the same start value (message object
number of the FIFO base element). CANPTR
<sl>
of all FIFO slave elements must be
initialized with the message object number of the FIFO base element. Bitfield FSIZE
<d>
of all FIFO elements must contain the FIFO buffer length and has to be identical with the
content of FSIZE
<s>
.
illustrates the operation of a normal gateway with a FIFO buffer on the
destination side.