ADSP-BF537 Blackfin Processor Hardware Reference
9-31
CAN Module
After having received 8 recessive bits, every node knows that the error con-
dition has been resolved and starts transmission if messages are pending.
The former transmitter that had to abort its operation must win the new
arbitration again, otherwise its message is delayed as determined by
priority.
Because the transmission of an error frame destroys the frame under trans-
mission, a faulty node erroneously detecting an error can block the bus.
Because of this, there are two node states which determine a node’s right
to signal an error—error active and error passive. Error active nodes are
those which have an error detection rate below a certain limit. These
nodes drive an ‘active error flag’ of 6 dominant bits.
Nodes with a higher error detection rate are suspected of having a local
problem and, therefore, have a limited right to signal errors. These error
passive nodes drive a ‘passive error flag’ consisting of 6 recessive bits.
Thus, an error passive transmitting node is still able to inform the other
nodes about the abortion of a self-transmitted frame, but it is no longer
able to destroy correctly received frames of other nodes.
Error Levels
The CAN specification requires each node in the system to operate in one
of three levels. See
. This prevents nodes with high error rates
from blocking the entire network, as the errors might be caused by local
hardware. The Blackfin CAN module provides an error counter for trans-
mit (
TEC
) and an error counter for receive (
REC
). The CAN error count
register
CAN_CEC
houses each of these 8-bit counters.
After initialization, both the
TEC
and the
REC
counters are 0. Each time a
bus error occurs, one of the counters is incremented by either 1 or 8,
depending on the error situation (documented in Version 2.0 of CAN
Specification). Successful transmit and receive operations decrement the
respective counter by 1.
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 ...