MC68HC08AZ60 Datasheet, PDF (326/452 Pages) Motorola, Inc – Advance Information

Freescale Semiconductor, Inc.
MSCAN Controller (MSCAN08)
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.
f_Tq =
f_MSCANCLK
Presc value
A bit time is subdivided into three segments¹(see Figure 8).
• 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–CBTR1, see MSCAN08 Bus Timing Register 0 on
page 340 and MSCAN08 Bus Timing Register 1 on page 341).
1. For further explanation of the underlying concepts please refer to ISO/DIS 11 519-1, Section
10.3.
MC68HC08AZ60 — Rev 1.0
326
MSCAN Controller (MSCAN08)
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