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): 152/157頁
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代理商: CR16HCS9VJE8Y
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152
26.0
Appendix
The following document describes problems identified in the
CR16 modules.
26.1
CR16CAN
26.1.1
Under certain conditions it occurs that the CR16CAN module
receives a frame, sent by itself even though the loopback fea-
ture is disabled.
This condition consists of two parts, which both must be true
to cause this malfunction.
A) The first part is that a transmit buffer and at least one re-
ceive buffer are configured with the same identifier. Let's call
this identifier ID_RX_TX here. With regard to the receive
buffer, this means that the buffer identifier and the corre-
sponding filter masks are setup in a way that the buffer is able
to receive frames with the identifier ID_RX_TX.
B) The second part is that the CAN communication must take
place in the following sequence:
1. A message with the identifier ID_RX_TX from another
CAN node is received into the receive buffer.
2. A message with the identifier ID_RX_TX is sent by the
CR16CAN module immediately after the reception took
place (Note).
After this communication the frame sent by the CR16CAN
module will be copied into the next receive buffer available
for the identifier ID_RX_TX.
Note:
If a frame with an identifier different to ID_RX_TX is
sent or received in between the steps 1 and 2, the problem
does not occur.
CR16CAN Problem Descriptions:
26.1.2
When a frame is received into the hidden receive buffer, the
CR16CAN module scans through all CAN message buffers.
During this sequence all receive buffers (RX-buffers) capable
of receiving this frame are tagged (RX-tag). If the message
was received correctly the frame is copied into first tagged
buffer (lowest buffer number).
Every CAN node also monitors frames being transmitted in
order to switch from transmitter to receiver after a lost arbitra-
tion. In order to do this the CR16CAN module also receives
transmitted frames into the hidden receive buffer.
The scanning sequence is also applied to transmitted
frames. This means, the identifier in the hidden receive buffer
is compared with the RX-buffer identifiers. As the identifier is
the same as with the last receive scanning sequence, the
RX-tags will not be changed.
A CAN buffer receive tag is only updated in the following cas-
es:
— A new scanning sequence has overwritten the old re-
ceive tags due to a different identifier mask under com-
parison.
— The CPU has changed the CAN buffer status in the
CNSTAT.ST-field to any value which disables the buffer
to receive a message (e.g. RX_NOT_ACTIVE or any
TX-state)
— The CPU has changed the CAN buffer identifier.
CR16CAN Problem Cause
Applied to the CAN communication sequence described
above, this means that the transmitted message, currently
present in the hidden receive buffer will be copied into the
same receive buffer and the message received from the oth-
er CAN node will be overwritten.
Example
Buffer Settings
Filter Masks:
GMSKB = 0x0000
GMSKX = 0x000F
Buffer configuration:
CAN Communication Sequence A:
(BUFFLOCK disabled)
1. Message sent from another CAN node received into
buffer 1.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. CPU reads out data from CAN buffer 1 and resets the
buffer state from RX_FULL to RX_READY (Note 1).
3. CAN buffer 0 sends a frame (status set to TX_ONCE).
4. Status of CAN buffer 1 changes to RX_FULL, because it
has received the message sent by buffer 0 (Note 2).
Note:
1. Step 2 does not need to be done. In case the buffer
1 status is not updated to RX_READY, the buffer status will
change from RX_FULL to RX_OVERRUN in step 4.
Note:
2. As BUFFLOCK is disabled, all messages with the
identifier ID_RX_TX will be copied into buffer 1. Buffer 2 does
not receive any message.
CAN Communication Sequence B:
(BUFFLOCK enabled)
1. Message sent from another CAN node received into
buffer 1. Buffer 1 is locked now.
Buffer 1 and buffer 2 are tagged for reception of this
message.
2. CAN buffer 0 sends a frame.
3. Status of CAN buffer 2 changes to RX_FULL, because it
has received the message sent by buffer 0.
CAN Communication Sequence C
(CR16CAN does NOT receive a frame sent by itself.)
CAN
Buffer
Number
CAN Buffer
Status
Buffer
Identifier
Identifier
Mask
0
TX_NOT_ACTIVE 0x15555550 0x1555555X
1
RX_READY
0x15555551 0x1555555X
2
RX_READY
0x15555552 0x1555555X
3
RX_READY
0x15555003 0x1555500X
X = don't care
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