XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 400

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

MSCAN Controller (MSCAN08)
Technical Data
400
NOTE:
The clock source has to be chosen such that the tight oscillator tolerance
requirements (up to 0.4%) of the CAN protocol are met.
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.
A bit time is subdivided into three segments
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.
•
•
•
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.
MSCAN Controller (MSCAN08)
Bit rate=
f
Tq
=
No. of time quanta
Presc value
f
MSCANCLK
f
Tq
(1)
MC68HC908AZ60A — Rev 2.0
(see
Figure
23-8).
MOTOROLA