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LH75400/01/10/11 (Preliminary) User’s Guide
Controller Area Network
6/17/03
22-9
22.3.2.2 Command Register
CMR is the Command Register. The active bits used in this register are Write Only. Setting
one or more of the usable bits starts an action in the CAN Controller’s transfer layer. Writ-
ing a 0 to any bit has no effect.
When using this register:
• All bits return 0 when this register is read.
• At least one system clock cycle is needed between consecutive commands.
• Setting bits [1] and [0] simultaneously results in single-shot transmission of the transmit
message without re-transmission in case an error or loss of arbitration occurs.
• Setting bits [4] and [1] simultaneously results in a single-shot transmission of the
Transmit message using the Self-Reception feature, again without re-transmission in
case of an error or arbitration loss.
• If bits [4] and [0] are set simultaneously, bit [4] is ignored.
• A transmission request made in a previous command cannot be cancelled by setting bit
[0] to 0. The requested transmission can only be cancelled by setting bit [1] to 1.
Table 22-4. CMR Register
BIT
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
FIELD
///
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
RW
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
FIELD
///
SRR
CDO
RRB
AT
TR
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
RW
R
R
R
R
R
R
R
R
R
R
R
W
W
W
W
W
ADDR
0xFF 0x04
Table 22-5. CMR Register Definitions
BIT
NAME
DESCRIPTION
31:5
///
Reserved
Writing to these bits has no effect. Reading returns 0.
4
SRR
Self-Reception Request
0 = No message is transmitted or received simultaneously.
1 = A message is transmitted and received simultaneously.
3
CDO
Clear Data Overrun
0 = Do not clear the data overrun condition signaled by the Data Overrun Status bit in the
Status Register.
1 = Clear the data overrun condition signaled by the Data Overrun Status bit (bit [1] of the
Status Register, described in Section 22.3.2.3).
Note that no further data overrun interrupt is generated while the Data Overrun Status bit
remains set.
2
RRB
Release Receive Buffer
0 = Do not release the Receive Buffer.
1 = Release the Receive Buffer.
1
AT
Abort Transmission
0 = Do not cancel the next transmission request.
1 = Cancel the next transmission request, provided it is not already in progress.
0
TR
Transmission Request
0 = No message is to be transmitted.
1 = A message is to be transmitted.