MC68HC08AZ16 Datasheet, PDF (368/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

msCAN08 Controller (msCAN08)
Clock system
Clock system
Figure 7shows the structure of the msCAN08 clock generation circuitry
and its interaction with the Clock Generation Module (CGM). With this
flexible clocking scheme the msCAN08 is able to handle CAN bus rates
ranging from 10 kbps up to 1 Mbps.
OSC
CGM
MSCAN08
/2
CGMXCLK
/2
PLL
/2
BCS
CGMOUT
(to SIM)
(2 * Bus Freq.)
MSCANCLK
CLKSRC
Prescaler
(1 .. 64)
time quanta clock
Figure 7. Clocking scheme
The Clock Source Flag (CLKSRC) in the msCAN08 Module Control
Register (CMCR1) (see msCAN08 module control register (CMCR1) on
page 379) defines whether the msCAN08 is connected to the output of
the crystal oscillator or to the PLL output.
A programmable prescaler is used to generate from the msCAN08 clock
the time quanta (Tq) clock. A time quantum is the atomic unit of time
handled by the msCAN08. A bit time is subdivided into three segments¹:
21-can
MOTOROLA
1. For further explanation of the under-lying concepts please refer to ISO/DIS 11519-1, Section
10.3.
msCAN08 Controller (msCAN08)
MC68HC08AZ32
367