Datasheet
UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 290 of 547
NXP Semiconductors
UM10398
Chapter 16: LPC111x/LPC11Cxx C_CAN controller
16.6.1.4 CAN bit timing register
[1] Hardware interprets the value programmed into these bits as the bit value 1.
For example, with a LPC11Cx system clock set to of 8 MHz, the reset value of 0x2301
configures the C_CAN for a bit rate of 500 kBit/s.
The registers are only writable if a configuration change is enabled in CANCTRL and the
controller is initialized by software (bits CCE and INIT in the CAN Control Register are
set).
For details on bit timing, see Section 16.7.5
and the Bosch C_CAN user’s manual,
revision 1.2.
Baud rate prescaler
The bit time quanta t
q
are determined by the BRP value:
t
q
= BRP / f
sys
(f
sys
is the LPC11Cx system clock to the C_CAN block).
Time segments 1 and 2
Time segments TSEG1 and TSEG2 determine the number of time quanta per bit time
and the location of the sample point:
t
TSEG1/2
= t
q
(TSEG1/2 + 1)
Synchronization jump width
To compensate for phase shifts between clock oscillators of different bus controllers, any
bus controller must re-synchronize on any relevant signal edge of the current
transmission. The synchronization jump width t
SJW
defines the maximum number of clock
cycles a certain bit period may be shortened or lengthened by one re-synchronization:
t
SJW
= t
q
(SJW + 1)
Table 249. CAN bit timing register (CANBT, address 0x4005 000C) bit description
Bit Symbol Description Reset
value
Access
5:0 BRP Baud rate prescaler
The value by which the oscillator frequency is divided for
generating the bit time quanta. The bit time is built up from
a multiple of this quanta. Valid values for the Baud Rate
Prescaler are 0 to 63.
[1]
000001 R/W
7:6 SJW (Re)synchronization jump width
Valid programmed values are 0 to 3.
[1]
00 R/W
11:8 TSEG1 Time segment before the sample point including
propagation segment.
Valid values are 1 to 15.
[1]
0011 R/W
14:12 TSEG2 Time segment after the sample point
Valid values are 0 to 7.
[1]
010 R/W
31:15 - Reserved - -