Users Guide: Network Microcontroller Supplement User Manual

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
163
The timing of the various time segments is determined by using the following formulae. Most users never need to perform these cal-
culations, as other devices already attached to the network dictate the bus timing parameters.
(Only integer values are permitted.)
Where BPRV is the CAN baud-rate prescaler value found in the earlier description of the C0BT0 register, F
OSC
is the crystal or external
oscillator frequency of the microprocessor, and TS1_LEN and TS2_LEN are listed in the description of the TSEG26-24 and TSEG13–10
bits in the CAN bus timing register 1. SJW is listed in the description of the SJW1-0 bits in the CAN bus timing register 0. The CAN clock
divide value (CCD) is a factor connected to the current microcontroller system clock selection and can be referenced in the following
table.
The following restrictions apply to the above equations:
t
TSEG1
≥ t
TSEG2
t
TSEG2
≥ t
SJW
t
SJW
< t
TSEG1
2 ≤ TS1_LEN ≤ 16
2 ≤ TS2_LEN ≤ 8
(TS1_LEN + TS2_LEN + 1) ≤ 25
The nominal bit time applies when a synchronization edge falls within the t
SYNC_SEG
period. The maximum bit time occurs when the syn-
chronization edge falls outside of the t
SYNC_SEG
period, and the synchronization jump width time is added to perform the resynchro-
nization.
Threefold Bit Sampling
The DS80C400 supports the ability to perform one or three samplings of each bit, based on the SMP bit (C0BT1.7). The single sample
mode (SMP = 0) is available in all settings and takes one sample during each bit time. The triple sampling mode (SMP = 1) samples
each bit three times for increased noise immunity. This mode can be used only when the baud-rate prescale value (BPRV) is greater
than 3.
No al bit time t t t
SYNC SEG TSEG TS
min   Ä Ä   
_
=++
1EEG
BRPV CCD TS LEN TS LEN
2
11 2
=
++( )( )[   ( _ )  ( _ )]
FFosc
Maximum bit time t t
SYNC SEG TSEG

_
=+
1
+++
=
+( )( )[   ( _ )
tt
BRPV CCD TS LEN
TSEG SJW2
11 +++
=
( _ )  ( )]
Ä
TS LEN SJW
Fosc
CANbaudrate
Fosc
2
(( )( )[   ( _ )  ( _ )BRPV CCD TS LEN TS LEN1 12++
CD1 CD0 4X/
22
22
XX
XX
CCD
0 0 1 0.5
0001
10x2
1 1 x 512
t
BRPV CCD
F
tt
t TS LEN t
t TS LEN t
t
t
BAUD RATE t
QU
OSC
SYNC SEG QU
TSEG QU
TSEG QU
SJW SJW t
QU PER BIT
QU
QU
(_ )
(_)
_
()
=
×
=×
=×
=×
=
×
=×
1
1
2
1
1
2
Maxim Integrated