S912XEG128J2VAL
| Model | S912XEG128J2VAL |
| Description | IC,MICROCONTROLLER,16-BIT,CPU12 CPU,CMOS,QFP,112PIN,PLASTIC |
| PDF file | Total 1327 pages (File size: 7M) |
| Chip Manufacturer | ROCHESTER |
Chapter 16 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.
Eqn. 16-2
Because of an order from the United States International Trade Commission, BGA-packaged product lines and part numbers indicated here currently are not
available from Freescale for import or sale in the United States prior to September 2010: S12XE products in 208 MAPBGA packages
f
CANCLK
= -----------------------------------------------------
Tq
(
Prescaler value -
)
A bit time is subdivided into three segments as described in the Bosch CAN specification. (see
Figure 16-
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.
Eqn. 16-3
f
Tq
Bit Rate = --------------------------------------------------------------------------------
-
(
number of Time Quanta
)
NRZ Signal
SYNC_SEG
Time Segment 1
(PROP_SEG + PHASE_SEG1)
4 ... 16
8 ... 25 Time Quanta
= 1 Bit Time
Time Segment 2
(PHASE_SEG2)
2 ... 8
1
Transmit Point
Sample Point
(single or triple sampling)
Figure 16-44. Segments within the Bit Time
MC9S12XE-Family Reference Manual , Rev. 1.19
648
Freescale Semiconductor
