cp3bt13 National Semiconductor Corporation, cp3bt13 Datasheet - Page 86

• Manufacturer Part Number: cp3bt13
• Description: Cp3bt13 Reprogrammable Connectivity Processor With Bluetooth-r And Can Interfaces
• Manufacturer: National Semiconductor Corporation

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buffer status field. With this lock function, software has the
capability to save several messages with the same identifier
or same identifier group into more than one buffer. For ex-
ample, a buffer with the second highest priority will receive
a message if the buffer with the highest priority has already
received a message and is now locked (provided that both
buffers use the same acceptance filtering mask).
16.5
All received frames are initially buffered in a hidden receive
buffer until the frame is valid. (The validation point for a re-
ceived message is the next-to-last bit of the EOF.) The re-
ceived identifier is then compared to every buffer ID
together with the respective mask and the status. As soon
as the validation point is reached, the whole contents of the
hidden buffer are copied into the matching message buffer
as shown in Figure 40.
RECEIVE STRUCTURE
BUFFER13_ID
BUFFER14_ID
BUFFER0_ID
BUFFER1_ID
Received ID
Figure 39. Message Storage with BUFFLOCK Enabled
GMASK
BMASK
01010
00000
01010
01010
01010
00000
01010
XXXXXXXX
XXXXXXXX
XXXXXXXX
XXXXXXXX
10101010
11111111
11111111
10101010
00000000
10101010
10101010
10101010
00000000
10101010
86
As shown in Figure 39, several messages with the same ID
are received while BUFFLOCK is enabled. The filtering
mask of the buffers 0, 1, 13, and 14 is set to accept this mes-
sage. The first incoming frame will be received by buffer 0.
Because buffer 0 is now locked, the next frame will be re-
ceived by buffer 1, and so on. If all matching receive buffers
are full and locked, a further incoming message will not be
received by any buffer.
Note: The hidden receive buffer must not be accessed by
the CPU.
The following section gives an overview of the reception of
the different types of frames.
The received data frame is stored in the first matching re-
ceive buffer beginning with buffer 0. For example, if the mes-
sage is accepted by buffer 5, then at the time the message
will be copied, the RX request is cleared and the CAN mod-
ule will not try to match the frame to any subsequent buffer.
10101010
00000000
10101010
10101010
10101010
00000000
10101010
CR16CAN
Figure 40. Receive Buffer
Saved when buffer
is empty
Saved when buffer
is empty
Saved when buffer
is empty
Saved when buffer
is empty
Receive
Hidden
Buffer
DS035
BUFFER_ID
BUFFER_ID
BUFFER_ID
Buffer 13
Buffer 14
Buffer 0
DS036