MC68HC08AZ32A Datasheet, PDF (343/456 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
MSCAN08 Controller (MSCAN08)
Clock System
CGMXCLK
OSC
CGM
MSCAN08
÷2
PLL
CLKSRC
÷2
CGMOUT
(TO SIM)
BCS
÷2
(2 * BUS FREQ.)
PRESCALER
(1 .. 64)
MSCANCLK
Figure 20-7. Clocking Scheme
The clock source bit (CLKSRC) in the MSCAN08 module control register
(CMCR1) (see MSCAN08 Module Control Register 0 on page 355)
defines whether the MSCAN08 is connected to the output of the crystal
oscillator or to the PLL output.
The clock source has to be chosen such that the tight oscillator tolerance
requirements (up to 0.4%) of the CAN protocol are met.
NOTE:
If the system clock is generated from a PLL, it is recommended to select
the crystal clock source rather than the system clock source due to jitter
considerations, especially at faster CAN bus rates.
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.
MC68HC08AZ32A — Rev 1.0
MOTOROLA
MSCAN08 Controller (MSCAN08)
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Technical Data
343