MC908GZ60CFUE Datasheet, PDF (148/352 Pages) Freescale Semiconductor, Inc – Standard features, Features of the CPU08

MSCAN08 Controller (MSCAN08)
CGMXCLK
OSC
CGM
MSCAN08
÷2
PLL
CLKSRC
÷2
CGMOUT
(TO SIM)
BCS
÷2
(2 * BUS FREQUENCY)
PRESCALER
(1 ... 64)
MSCANCLK
Figure 12-8. Clocking Scheme
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.
1. For further explanation of the underlying concepts please refer to ISO/DIS 11 519-1,
Section 10.3.
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
148
Freescale Semiconductor