RX610 Group
7. Clock Generation Circuit
R01UH0032EJ0120 Rev.1.20
Page 167 of 1006
Feb 20, 2013
7.7
Usage Notes
7.7.1
Notes on the Clock Generation Circuit
1. The frequencies of the system clock (ICLK), peripheral module clock (PCLK), and external bus clock (BCLK)
supplied to each module are selected according to the setting of SCKCR. Select each frequency that is within the
operation guaranteed range of clock cycle time (tcyc) specified in AC characteristics of electrical characteristics.
Each frequency should meet the following:
ICLK = 8 to 100 MHz, PCLK = 8 to 50 MHz, BCLK = 8 to 25 MHz
All peripheral modules (except for the DMAC and DTC) operate on the PCLK. Note therefore that the operating
speed of modules such as the timer and SCI varies before and after the frequency is changed.
In addition, the waiting time for canceling software standby mode varies with the frequency change. For details, see
section 8.5.3.3, Setting Oscillation Settling Time after Software Standby Mode is Canceled.
2. The relationship among the system clock (ICLK), peripheral module clock (PCLK), and external bus clock (BCLK)
is ICLK
≥
PCLK and ICLK
≥
BCLK, and the ICLK has the highest priority. For this reason, if a setting that does
not meet these conditions is made, the PCLK and BCLK may have the clock frequency set by the ICK[3:0] bits in
SCKCR regardless of the settings of the PCK[3:0] and BCK[3:0] bits in SCKCR.
3. Note that when changing a clock frequency, it may change during an access to the external bus.
4. After writing to the SCKCR, further writing to the same register before completion of the change in frequency is
ignored. In the case of continued writing to the SCKCR, confirm that values read from the SCKCR are actually the
most recently written values.
5. After writing to the SCKCR, transitions to software standby mode are prohibited until completion of the change in
frequency. Subsequent operation is not guaranteed if a transition to software standby mode is attempted while the
frequency is being changed. The interval between writing to the SCKCR and issuing of the WAIT instruction must
take up at least 11 cycles of the system clock.