MCP2510-SLASHST datasheet(39/80 Pages) MICROCHIP

39 / 80 page

DS21291F-page 39

MCP2510

5.10

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).

5.10.1

CNF1

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 synchroni-

zation jump width in terms of number of TQ’s.

5.10.2

CNF2

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).

5.10.3

CNF3

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/W-0

SJW1

SJW0

BRP5

BRP4

BRP3

BRP2

BRP1

BRP0

bit 7

bit 0

bit 7-6

SJW<1:0>: Synchronization Jump Width Length

= Length = 4 x TQ

= Length = 3 x TQ

= Length = 2 x TQ

= Length = 1 x TQ

bit 5-0

BRP<5:0>: Baud Rate Prescaler

TQ = 2 x (BRP + 1) / FOSC

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

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