Section 18 Clock Pulse Generator
Rev. 3.00 Mar. 14, 2006 Page 667 of 804
REJ09B0104-0300
18.5 Usage
Notes
18.5.1
Notes on Clock Pulse Generator
1. The following points should be noted since the frequency of
φ
(I
φ
: system clock and P
φ
:
peripheral module clock) supplied to each module changes according to the setting of SCKCR.
Select a clock division ratio that is within the operation guaranteed range of clock cycle time
t
cyc
shown in the AC timing of electrical characteristics.
When the HCAN and SSU are in use, 8 MHz
≤
I
φ
≤
40 MHz, and 8 MHz
≤
P
φ
≤
20 MHz, the
following settings are not permitted: I
φ
< 8MHz, I
φ
> 40 MHz, P
φ
< 8MHz, and P
φ
> 20 MHz.
When the HCAN and SSU are not in use, 8 MHz
≤
I
φ
≤
40 MHz, and 8 MHz
≤
P
φ
≤
35 MHz,
the following settings are not permitted: I
φ
< 8MHz, I
φ
> 40 MHz, P
φ
< 8MHz, and P
φ
> 35
MHz.
2. All the on-chip peripheral modules (except for the DMAC) operate on the P
φ
. Therefore, note
that the time processing of modules such as a timer and SCI differs before and after changing
the clock division ratio.
In addition, wait time for clearing software standby mode differs by changing the clock
division ratio. For details, see section 19.7.3, Setting Oscillation Settling Time after Clearing
Software Standby Mode.
3. The relationship between the system clock and peripheral module clock is I
φ
≥
P
φ
. In addition,
the system clock setting has priority. Accordingly, P
φ
may have the frequency set by bits ICK2
to ICK0 regardless of the settings of bits PCK2 to PCK0.
4. Figure 18.5 shows the clock modification timing. After a value is written to SCKCR, this LSI
waits for the current bus cycle to complete. After the current bus cycle completes, each clock
frequency will be modified within one cycle (worst case) of the external clock.
External
clock
One cycle (worst case)
after the bus cycle completion
Operating clock
specified in SCKCR
Operating clock changed
I
φ
CPU
CPU
CPU
Bus master
Figure 18.5 Clock Modification Timing
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