Functional Operation
9-32
ADSP-BF537 Blackfin Processor Hardware Reference
If either of the error counters exceeds 127, the CAN module goes into a
passive state and the CAN error passive mode (
EP
) bit in
CAN_STATUS
is set.
Then, it is not allowed to send any more active error frames. However, it
is still allowed to transmit messages and to signal passive error frames in
case the transmission fails because of a bit error.
If one of the counters exceeds 255 (that is, when the 8-bit counters over-
flow), the CAN module is disconnected from the bus. It goes into bus off
mode and the CAN error bus off mode (
EBO
) bit is set in
CAN_STATUS
. Soft-
ware intervention is required to recover from this state.
In addition to these levels, the CAN module also provides a warning
mechanism, which is an enhancement to the CAN specification. There are
separate warnings for transmit and receive. By default, when one of the
error counters exceeds 96, a warning is signaled and is represented in the
CAN_STATUS
register by either the CAN receive warning flag (
WR
) or CAN
transmit warning flag (
WT
) bits. The error warning level can be pro-
grammed using the error warning register,
CAN_EWR
. More information is
.
Table 9-3. CAN Error Level Description
Level
Condition
Description
Error active
Transmit and receive error
counters
<
128
This is the initial condition level. As
long as errors stay below 128, the
node will drive active error flags dur-
ing error frames.
Error passive
Transmit or receive error
counters
≥
128, but
<
256
Errors have accumulated to a level
which requires the node to drive pas-
sive error flags during error frames.
Bus off
Transmit or receive error
counters
≥
256
CAN module goes into bus off mode
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...