TMP91CW60DFG datasheet(18/262 Pages) TOSHIBA

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Page 15

2007-12-03

TMP91CW60

2.3.3

System Clock Controller

The system clock controller generates the system clock signal (fSYS) for the CPU core and internal I/O.It

contains two oscillation circuits and a clock gear circuit for high-frequency (fc) operation. The register

SYSCR1<SYSCK> changes the system clock to either fc or fs, SYSCR0<XEN> and SYSCR0<XTEN> con-

trol enabling and disabling of each oscillator, and SYSCR1<GEAR2:0> sets the high-frequency clock gear to

either 1, 2, 4, 8 or 16 (fc, fc/2, fc/4, fc/8 or fc/16). These functions can reduce the power consumption of the

equipment in which the device is installed.

The combination of settings <XEN> = "1", <XTEN> = "0", <SYSCK> = "0" and <GEAR2:0> = "000" will

cause the system clock (fSYS) to be set to fc/2 (=fc x 1/2) after a Reset. For example, fSYS is set to 8 MHz when

the 16 MHz oscillator connected to the X1 and X2 pins.

(1) Switching from NORMAL mode to SLOW mode

When the resonator is connected to the X1 and X2 pins, or to the XT1 and XT2 pins, the warm-up timer

can be used to change the operation frequency after stable oscillation has been attained.

The warm-up time can be selected using SYSCR2<WUPTM1:0>.

This warm-up timer can be programmed to start and stop as shown in the following examples 1 and 2.

Table 2-2 shows the warm-up time.

Note 1: When using an oscillator (other than a resonator) with stable oscillation, a warm-up timer is not needed.

Note 2: The warm-up timer is operated by an oscillation clock. Hence, there may be some variation in warm-up

time.

Note 3: Note of using low-frequency oscillator

When connect low-frequency oscillator to ports 96 and 97, need below setting for cut consumption power.

(Case of resonators)

Set P9CR<P96C, P97C> = "11", P9<P96:97> = "00"

(Case of oscillator)

Set P9CR<P96C, P97C> = "11", P9<P96:97> = "10"

Note: At fOSCH=20MHz，fs=32.768kHz

Table 2-2

Warm-up Times (when changing clock)

Select Warm-up Time

SYSCR2<WUPTM1:0>

Change to NORMAL (fc)

Change to SLOW (fs)

01(28/frequency)

12.8[us]

7.8[ms]

10(214/frequency)

0.819[ms]

500[ms]

11(216/frequency)

3.277[ms]

2000[ms]

00(218/frequency)

13.107[ms]

8000[ms]

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