CAN Operation
9-20
ADSP-BF537 Blackfin Processor Hardware Reference
Upon programming the universal counter to watchdog mode (set
UCCNF[3:0]
=
0x2
in
CAN_UCCNF
), the counter in the
CAN_UCCNT
register is
loaded with the predefined value contained in the CAN universal counter
reload/capture register (
CAN_UCRC
). This counter then decrements at the
CAN bit rate. If the
UCCT
and
UCRC
bits in the
CAN_UCCNF
register are set
and a message is received in mailbox 4 before the counter counts down to
0, the counter is reloaded with the
CAN_UCRC
contents. If the counter has
counted down to 0 without receiving a message in mailbox 4, the
UCEIS
bit in the global interrupt status (
CAN_GIS
) register is set, and the counter
is automatically reloaded with the contents of the
CAN_UCRC
register. If an
interrupt is desired, the
UCEIM
bit in the
CAN_GIM
register must also be set.
With the mask bit set, when a watchdog interrupt occurs, the
UCEIF
bit in
the
CAN_GIF
register is also set.
The counter can be reloaded with the contents of
CAN_UCRC
or disabled by
writing to the
CAN_UCCNF
register.
The time period it takes for the watchdog interrupt to occur is controlled
by the value written into the
CAN_UCRC
register by the user.
Time Stamps
To get an indication of the time of reception or the time of transmission
for each message, program the CAN universal counter to time stamp
mode (set
UCCNF[3:0]
=
0x1
in
CAN_UCCNF
). The value of the 16-bit
free-running counter (
CAN_UCCNT
) is then written into the
CAN_MBxx_TIMESTAMP
register of the corresponding mailbox when a
received message has been stored or a message has been transmitted.
The time stamp value is captured at the sample point of the start of frame
(SOF) bit of each incoming or outgoing message. Afterwards, this time
stamp value is copied to the
CAN_MBxx_TIMESTAMP
register of the corre-
sponding mailbox.
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 ...