參數(shù)資料
型號： CR16HCS9VJE8Y
英文描述： Microcontroller
中文描述： 微控制器
文件頁數(shù)： 95/157頁
文件大小： 1256K
代理商： CR16HCS9VJE8Y
95
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20.3
The CR16CAN has access to 15 independent message buff-
ers, memory mapped in RAM. Each message buffer consists
of 8 different 16-bit RAM locations and can be individually
configured as a receive message buffer or as a transmit mes-
sage buffer.
A dedicated acceptance filtering procedure enables the user
to configure each buffer to receive only a single message ID
or a group of messages. One buffer uses an independent fil-
tering procedure, which provides the possibility to establish a
BASIC-CAN path.
For reception of data frame or remote frames, the CR16CAN
follows a “receive on first match” rule which means that a giv-
en message is only received by one buffer — the first one
which matches to the received message ID.
The transmission of a frame can be initiated by the user soft-
ware writing to the transmit status and priority register. An al-
ternate way to schedule a transmission is the automatic
answer to remote frames. In the latter case, the CR16CAN
will schedule every buffer for transmission to respond to re-
mote frames with a given identifier if the acceptance mask
matches. This implies that a single remote frame is able to
poll multiple matching buffers configured to respond to the
triggering remote transmission request.
MESSAGE TRANSFER
20.4
Two 32-bit masks are used to filter unwanted messages from
the CAN bus GMASK and BMASK. Figure 56 shows the
mask and the buffers controlled by the masks.
ACCEPTANCE FILTERING
The acceptance filtering of the incoming messages for the
buffers 0...13 is done by means of a global filtering mask
(GMASK) and by the buffer ID of each buffer.
The acceptance filtering of incoming messages for buffer 14
is done via a separate filtering mask (BMASK) and by the
buffer ID of each that buffer.
Once a received object is waiting in the hidden buffer (see
Receive Buffer Structure on page 97) to be copied into a buff-
er, CR16CAN scans all buffer configured as receive buffers
for a matching filtering mask. The buffers 0 to 13 are checked
in ascending order beginning with buffer 0. The contents of
the hidden buffer are copied into the first buffer with matching
filtering mask.
Bits holding a “1” in the global filtering mask (GMASK) can be
represented as a “don’t care” of the associated bit of each
buffer identifier, regardless of whether the buffer identifier bit
is “1” or “0”.
This provides the capability to accept only a single ID per
buffer or to accept a group of IDs. The following two exam-
ples illustrate the difference.
Example 1: Acceptance of a Single Identifier
If the global mask is set to 00
16
the acceptance filtering of an
incoming message is only determined by the individual buffer
ID. This means that only one message ID is accepted per
buffer.
Example 2: Reception of an Identifier Group
Bits in the global mask register set to ‘1’ change the corre-
sponding bit status within the buffer ID to “don’t care” (“X”).
Therefore all messages which match the non-“don’t care”
bits are accepted.
Buffer 0
Buffer13
Buffer14
GMASK1
GMASK2
BMASK1
BMASK2
BUFFER_ID
BUFFER_ID
BUFFER_ID
Figure 56.
Acceptance Filtering Structure
GMASK1
GMASK2
BUFFER_ID1
10101010
BUFFER_ID2
10101
00000000
00000000
00000000
00000
10101010
10101010
10101010
10101010
10101010
10101
Accepted ID
Figure 57.
Acceptance of a Single Identifier
GMASK1
GMASK2
BUFFER_ID1
10101010
BUFFER_ID2
00000000
00000000
00000
10101010
10101010
10101010
XXXXXXXX
10101010
Accepted ID group
10101
10101
Figure 58.
Acceptance of a Group of Identifiers
11111111
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