Hitachi H8S/2646 Hardware Manual page 10

Section Page
15.3.2 Initialization 565 to
after Hardware 567
Reset
Bit Rate and Bit
Timing Settings
Description
Example: With a 1 Mb/s baud rate and a 20 MHz input clock:
20 MHz
1 Mb/s =
2 × (0 + 1) × (3 + 4 + 3)
Set Values
f = 20 MHz
CLK
BRP = 0 (B'000000)
TSEG1 = 4 (B'0100)
TSEG2 = 3 (B'011)
1-bit time
SYNC_SEG
1
Legend
SYNC_SEG: Segment for establishing synchronization of nodes on the CAN bus. (Normal
bit edge transitions occur in this segment.)
PRSEG: Segment for compensating for physical delay between networks.
PHSEG1: Buffer segment for correcting phase drift (positive). (This segment is extended
when synchronization (resynchronization) is established.)
PHSEG2: Buffer segment for correcting phase drift (negative). (This segment is
shortened when synchronization (resynchronization) is established.)
Note: The time quanta values of TSEG1 and TSEG2 become the value of TSEG + 1.
Figure 15-6 Detailed Description of Timing within 1 Bit
HCAN bit rate calculation:
Bit rate =
2 × (BRP + 1) × (3 + TSEG1 + TSEG2)
Note: f = ø (system clock)
CLK
The BCR values are used for BRP, TSEG1, and TSEG2.
BCR Setting Constraints
TSEG1 > TSEG2 ≥ SJW
These constraints allow the setting range shown in table 15-4 for TSEG1 and TSEG2 in BCR.
Table 15-4 Setting Range for TSEG1 and TSEG2 in BCR
001
TSEG1 0011 No
(BCR [11:8])
0100 Yes*
0101 Yes*
0110 Yes*
0111 Yes*
1000 Yes*
1001 Yes*
1010 Yes*
1011 Yes*
1100 Yes*
1101 Yes*
1110 Yes*
1111 Yes*
Notes: The time quanta value for TSEG1 and TSEG2 is the TSEG value + 1.
* Only a value other than BRP[13:8] = B'000000 can be set.
Actual Values
—
System clock × 2
5TQ
4TQ
1-bit time (8–25 time quanta)
PRSEG PHSEG1
TSEG1 (time segment 1)
2–16
f
CLK
(SJW = 0 to 3)
TSEG2 (BCR [14:12])
010 011 100 101
Yes No No No
Yes Yes No No
Yes Yes Yes No
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Yes Yes Yes
PHSEG2
TSEG2 (time segment 2)
Quantum
2–8
110 111
No No
No No
No No
No No
Yes No
Yes Yes
Yes Yes
Yes Yes
Yes Yes
Yes Yes
Yes Yes
Yes Yes
Yes Yes