M16CSLASH26 datasheet(37/239 Pages) RENESAS

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Clock Generating Circuit

Renesas Technology Corp.

M16C/26 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Under

development

Preliminary Specifications Rev. 0.9

Specifications in this manual are tentative and subject to change.

The following paragraphs describes the clocks generated by the clock generating circuit.

(1) Main clock

The main clock is generated by the main clock oscillation circuit. After a reset, the clock is divided by 8 to

the BCLK. The clock can be stopped using the main clock stop bit (bit 5 at address 000616). Stopping the

clock, after switching the operating clock source of CPU to the sub-clock, reduces the power dissipation.

After the oscillation of the main clock oscillation circuit has stabilized, the drive capacity of the main clock

oscillation circuit can be reduced using the XIN-XOUT drive capacity select bit (bit 5 at address 000716).

Reducing the drive capacity of the main clock oscillation circuit reduces the power dissipation. This bit

changes to “1” when shifting from high-speed/medium-speed mode to stop mode, shifting to low power

dissipation mode and at a reset. When shifting from high-speed/medium-speed mode to low-speed

mode, the value before high-speed/medium-speed mode is retained.

(2) Sub-clock

The sub-clock is generated by the sub-clock oscillation circuit. No sub-clock is generated after a reset.

After oscillation is started using the port XC select bit (bit 4 at address 000616), the sub-clock can be

selected as the BCLK by using the system clock select bit (bit 7 at address 000616). However, be sure

that the sub-clock oscillation has fully stabilized before switching.

After the oscillation of the sub-clock oscillation circuit has stabilized, the drive capacity of the sub-clock

oscillation circuit can be reduced using the XCIN-XCOUT drive capacity select bit (bit 3 at address 000616).

Reducing the drive capacity of the sub-clock oscillation circuit reduces the power dissipation. This bit

changes to “1” when the port XC select bit (bit 4 at address 000616) is set to “0” , shifting to stop mode and

at a reset.

When the XCIN/XCOUT is used, set ports P86 and P87 as the input ports without pull-up.

(3) BCLK

The BCLK is the clock that drives the CPU, and is fC or the clock is derived by dividing the main clock by

1, 2, 4, 8, or 16. The BCLK is derived by dividing the main clock by 8 after a reset.

The main clock division select bit 0(bit 6 at address 000616) changes to “1” when shifting from high-

speed/medium-speed to stop mode, shifting to low power dissipation mode and at reset. When shifting

from high-speed/medium-speed mode to low-speed mode, the value before high-speed/medium-speed

mode is retained.

(4) Peripheral function clock(f1, f8, f32, f1SIO2, f8SIO2,f32SIO2,fAD)

The clock for the peripheral devices is derived from the main clock or by dividing it by 1, 8, or 32. The

peripheral function clock is stopped by stopping the main clock or by setting the WAIT peripheral function

clock stop bit (bit 2 at 000616) to “1” and then executing a WAIT instruction.

By setting the timer A, B clock select bit (bit 0 at address 001E16) and SIO clock select bit (bit 1 at address

001E16) to "1" respectively, f1 and f1SIO2 can be changed to the main clock divided by 2.

(5) fC32

This clock is derived by dividing the sub-clock by 32. It is used for the timer A and timer B counts.

(6) fC

This clock has the same frequency as the sub-clock. It is used for the BCLK and for the watchdog timer.

Figure 1.8.4a shows the system clock control registers 0 and 1 and Figure 1.8.4b shows peripheral clock

select register.

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