2000 Microchip Technology Inc.
Bit Timing Configuration Registers
The configuration registers (CNF1, CNF2, CNF3) con-
trol the bit timing for the CAN bus interface. These reg-
isters can only be modified when the MCP2510 is in
configuration mode (see Section 9.0).
The BRP<5:0> bits control the baud rate prescaler.
These bits set the length of TQ relative to the OSC1
input frequency, with the minimum length of TQ being 2
OSC1 clock cycles in length (when BRP<5:0> are set
to 000000). The SJW<1:0> bits select the synchroniza-
tion jump width in terms of number of TQ’s.
The PRSEG<2:0> bits set the length, in TQ’s, of the
propagation segment. The PHSEG1<2:0> bits set the
length, in TQ’s, of phase segment 1. The SAM bit con-
trols how many times the RXCAN pin is sampled. Set-
ting this bit to a ‘1’ causes the bus to be sampled three
times; twice at TQ/2 before the sample point, and once
at the normal sample point (which is at the end of phase
segment 1). The value of the bus is determined to be
the value read during at least two of the samples. If the
SAM bit is set to a ‘0’ then the RXCAN pin is sampled
only once at the sample point. The BTLMODE bit con-
trols how the length of phase segment 2 is determined.
If this bit is set to a ‘1’ then the length of phase segment
2 is determined by the PHSEG2<2:0> bits of CNF3
(see Section 5.10.3). If the BTLMODE bit is set to a ‘0’
then the length of phase segment 2 is the greater of
phase segment 1 and the information processing time
(which is fixed at 2 TQ for the MCP2510).
The PHSEG2<2:0> bits set the length, in TQ’s, of
Phase Segment 2, if the CNF2.BTLMODE bit is set to
a ‘1’. If the BTLMODE bit is set to a ‘0’ then the
PHSEG2<2:0> bits have no effect.
CNF1 - Configuration Register1 (ADDRESS: 2Ah)
R = Readable bit
W = Writable bit
C = Bit can be cleared by
MCU but not set
U = Unimplemented -
reads as ‘0’
- n = Value at POR reset
SJW<1:0>: Synchronization Jump Width Length
11 = Length = 4 x TQ
10 = Length = 3 x TQ
01 = Length = 2 x TQ
00 = Length = 1 x TQ
bit 5-0: BRP<5:0>: Baud Rate Prescaler
111111 = TQ = 2 x 64 x 1/FOSC
000000 = TQ = 2 x 1 x 1/FOSC