MC9S12HY64 Datasheet, PDF (351/792 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

Freescale’s Scalable Controller Area Network (S12MSCANV3)
For microcontrollers without a clock and reset generator (CRG), CANCLK is driven from the crystal
oscillator (oscillator clock).
A programmable prescaler generates the time quanta (Tq) clock from CANCLK. A time quantum is the
atomic unit of time handled by the MSCAN.
Tq= ₍^{---P----r---e----s-f--c-C---aA----lN--e--C-r---L---v-K--a----l--u----e----}₎
Eqn. 9-2
A bit time is subdivided into three segments as described in the Bosch CAN specification. (see Figure 9-
44):
• 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 the PHASE_SEG2 of the CAN standard. It can be
programmed by setting the TSEG2 parameter to be 2 to 8 time quanta long.
Bit Rate= ₍---n----u----m------b----e---r------o----f---f--T^T---^q-i--m-----e-------Q-----u----a----n----t--a----₎
Eqn. 9-3
NRZ Signal
SYNC_SEG
Time Segment 1
(PROP_SEG + PHASE_SEG1)
Time Segment 2
(PHASE_SEG2)
1
4 ... 16
8 ... 25 Time Quanta
= 1 Bit Time
2 ... 8
Transmit Point
Sample Point
(single or triple sampling)
Figure 9-44. Segments within the Bit Time
MC9S12HY/HA-Family Reference Manual Rev. 1.04
Freescale Semiconductor
351