DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
303 of 571
NXP Semiconductors
UM10316
Chapter 21: LPC29xx CAN 0/1
4.
CAN bus timing
4.1 Baud-rate prescaler
The period of the CAN system clock, t
scl
, is programmable and determines individual bit
timing. The CAN system clock is calculated using the following equation:
BRP is the baud-rate prescaler value defined in the bus timing register CCBT.
4.2 Synchronization jump width
To compensate for phase shifts between the clock oscillators of different bus controllers,
any bus controller must resynchronize on any relevant signal edge of the current
transmission. The synchronization jump-width defines the maximum number of clock
cycles by which a certain bit period can be shortened or lengthened during one
resynchronization:
SJW is the synchronization jump-width value defined in the bus timing register CCBT.
4.3 Time segments 1 and 2
Time segments TSEG1 and TSEG2 determine the number of clock cycles per bit-period
and the location of the sampling point:
TSEG1 and TSEG2 are timing-segment 1 and 2 values defined in CCBT. For
determination of bit-timing parameters see also
.
t
scl
BRP
1
+
fclk sys
(
)
----------------------
=
tsjw
tscl SJW
1
+
(
)
=
tSYNCSEG
1tscl
=
tTSEG1
tscl TSEG1
1
+
(
)
=
tTSEG2
tscl TSEG2
1
+
(
)
=