MC68HC08GZ32 Datasheet, PDF (128/320 Pages) Freescale Semiconductor, Inc – Microcontrollers

MSCAN08 Controller (MSCAN08)
A programmable prescaler is used to generate out of the MSCAN08 clock the time quanta (Tq) clock. A
time quantum is the atomic unit of time handled by the MSCAN08.
f_Tq =
f_MSCANCLK
Presc value
A bit time is subdivided into three segments⁽¹⁾ (see Figure 12-9):
• SYNC_SEG: This segment has a fixed length of one time quantum. Signal edges are expected to
happen within this section.
• Time segment 1: This segment includes the PROP_SEG and the PHASE_SEG1 of the CAN
standard. It can be programmed by setting the parameter TSEG1 to consist of 4 to 16 time quanta.
• Time segment 2: This segment represents PHASE_SEG2 of the CAN standard. It can be
programmed by setting the TSEG2 parameter to be 2 to 8 time quanta long.
f_Tq
Bit rate =
No. of time quanta
The synchronization jump width (SJW) can be programmed in a range of 1 to 4 time quanta by setting the
SJW parameter.
The above parameters can be set by programming the bus timing registers, CBTR0 and CBTR1. See
12.13.3 MSCAN08 Bus Timing Register 0 and 12.13.4 MSCAN08 Bus Timing Register 1.
NOTE
It is the user’s responsibility to make sure that the bit timing settings are in
compliance with the CAN standard,
Table 12-8 gives an overview on the CAN conforming segment settings and the related parameter values.
NRZ SIGNAL
SYNC
_SEG
1
TIME SEGMENT 1
(PROP_SEG + PHASE_SEG1)
TIME SEG. 2
(PHASE_SEG2)
4 ... 16
2 ... 8
8... 25 TIME QUANTA
= 1 BIT TIME
SAMPLE POINT
(SINGLE OR TRIPLE SAMPLING)
Figure 12-9. Segments Within the Bit Time
1. For further explanation of the underlying concepts please refer to ISO/DIS 11 519-1,
Section 10.3.
MC68HC08GZ32 Data Sheet, Rev. 3
128
Freescale Semiconductor