ADSP-BF537 Blackfin Processor Hardware Reference
9-11
CAN Module
The Blackfin CAN module does not distinguish between the propagation
segment and the phase segment 1 as defined by the standard. The
TSEG1
value is intended to cover both of them. The
TSEG2
value represents the
phase segment 2.
If the CAN module detects a signal edge outside the synchronization seg-
ment, it can automatically move the sampling point such that the CAN
bit is still handled properly. The synchronization jump width (
SJW
) field
specifies the maximum number of TQs, ranging from 1 to 4 (
SJW
+
1
),
allowed for such a resynchronization attempt. The
SJW
value should not
exceed
TSEG2
or
TSEG1
. Therefore, the fundamental rule for writing
CAN_TIMING
is:
SJW
<=
TSEG2
<=
TSEG1
In addition to this fundamental rule, phase segment 2 must also be greater
than or equal to the Information Processing Time (IPT). This is the time
required by the logic to sample
CANRX
input. On the Blackfin CAN mod-
ule, this is 3
SCLK
cycles. Because of this, restrictions apply to the minimal
value of
TSEG2
if the clock prescaler
BRP
is lower than 2. If
BRP
is set to 0,
the
TSEG2
field must be greater than or equal to 2. If the prescaler is set to
1, the minimum
TSEG2
is 1.
L
All nodes on a CAN bus should use the same nominal bit rate.
With all the timing parameters set, the final consideration is how sam-
pling is performed. The default behavior of the CAN controller is to
sample the CAN bit once at the sampling point described by the
CAN_TIMING
register, controlled by the
SAM
bit. If the
SAM
bit is set, how-
ever, the input signal is oversampled three times at the
SCLK
rate. The
resulting value is generated by a majority decision of the three sample val-
ues. Always keep the
SAM
bit cleared if the
BRP
value is less than 4.
Do not modify the
CAN_CLOCK
or
CAN_TIMING
registers during normal oper-
ation. Always enter configuration mode first. Writes to these registers have
no effect if not in configuration or debug mode. If not coming out or
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 ...