National CP3BT26 Can Error Counter Register Canec, Can Error Diagnostic Register Cediag, EFID30

19.10.15 CAN Error Counter Register (CANEC)

The CANEC register reports the values of the CAN Receive Error Counter and the CAN Transmit Error Counter.

15	8	7	0
	REC		TEC
	0
				EBID
	R
REC	The CAN Receive Error Counter field reports
	the value of the receive error counter.
TEC	The CAN Transmit Error Counter field reports
	the value of the transmit error counter.

19.10.16 CAN Error Diagnostic Register (CEDIAG)

The CEDIAG register reports information about the last de- tected error. The CAN module identifies the field within the CAN frame format in which the error occurred, and it identi- fies the bit number of the erroneous bit within the frame field. The CPU bus master has read-only access to this reg- ister, and all bits are cleared on reset.

15

14

13

12

11

10

9

4

3

0

Res.

DRIVE

MON

CRC

STUFF

TXE

EBID

EFID

0

R

EFID

The Error Field Identifier field

identifies the

frame field in which the last error occurred.

The encoding of the frame fields is shown in

Table 63.

Table 63 Error Field Identifier

TXE

EFID3:0

Field

0000

ERROR

0001

ERROR DEL

0010

ERROR ECHO

STUFF

0011

BUS IDLE

0100

ACK

0101

EOF

0110

INTERMISSION

0111

SUSPEND

TRANSMISSION

CRC

1000

SOF

1001

ARBITRATION

1010

IDE

1011

EXTENDED

ARBITRATION

MON

1100

R1/R0

Table 63 Error Field Identifier

EFID3:0	Field
1101	DLC
1110	DATA
1111	CRC

The Error Bit Identifier field reports the bit po- sition of the incorrect bit within the erroneous frame field. The bit number starts with the val- ue equal to the respective frame field length minus one at the beginning of each field and is decremented with each CAN bit. Figure 63 shows an example on how the EBID is calcu- lated.

r r r r r r

Incorrect

Bit

Data Field

DS047

Figure 63. EBID Example

For example, assume the EFID field shows 1110b and the EBID field shows 111001b. This means the faulty field was the data field. To calculate the bit position of the error, the DLC of the message needs to be known. For example, for a DLC of 8 data bytes, the bit counter starts with the value: (8 × 8) - 1 = 63; so when EBID[5:0] = 111001b = 57, then the bit number was 63 - 57 = 6.

The Transmit Error bit indicates whether the CAN module was an active transmitter at the time the error occurred.

0 – The CAN module was a receiver at the time the error occurred.

1 – The CAN module was an active transmit- ter at the time the error occurred.

The Stuff Error bit indicates whether the bit stuffing rule was violated at the time the error occurred. Note that certain bit fields do not use bit stuffing and therefore this bit may be ignored for those fields.

0 – No bit stuffing error.

1 – The bit stuffing rule was violated at the time the error occurred.

The CRC Error bit indicates whether the CRC is invalid. This bit should only be checked if the EFID field shows the code of the ACK field.

0 – No CRC error occurred.

1 – CRC error occurred.

The Monitor bit shows the bus value on the CANRX pin as sampled by the CAN module at the time of the error.

CP3BT26

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