DS80C390_00 Datasheet, PDF (150/155 Pages) Dallas Semiconductor – High-Speed Microcontroller User’s Guide Supplement

DS80C390 High-Speed Microcontroller User’s Guide Supplement
Timing Registers should never be written with all zeros. To prevent this the SWINT is forced to 0 when
TSEG1 = TSEG2 = 00h.
The timing of the various time segments is determined via the following formulae. Most users will never
need to perform these calculations, as other devices already attached to the network will dictate the bus
timing parameters.
tQU
=
BRPV ⋅ CCD
FOSC
tSYNC _ SEG = 1⋅ tQU
tTSEG1 = (TS1_ LEN) ⋅ tQU
tTSEG2 = (TS2 _ LEN) ⋅ tQU
tSJW = (SJW) ⋅ tQU
tQU per bit =
1
baud rate ⋅ tQU
(only integer values are permitted.)
where BPRV is the CAN baud rate prescaler value found in the description of the C0BT0/C1BT0
registers, 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
CCD is the CAN clock divide value, calculated from the following table.
CD1
0
0
1
1
CD0
0
0
0
1
4X/ 2X
1
0
x
x
CCD
0.5
1
2
512
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 synchronization edge falls outside of the t_{SYNC_SEG} period, and the
synchronization jump width time is added to perform the resynchronization.
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