TMP93CS41 datasheet(20/248 Pages) TOSHIBA

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TMP93CS40/TMP93CS41

2004-02-10

93CS40-18

3.3.1

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). The register SYSCR1<SYSCK> changes the system clock to either fc or fs,

SYSCR0<XEN> and SYSCR0<XTEN> control enabling and disabling each oscillator, and

SYSCR1<GEAR2:0> changes 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 system clock (fSYS) is set to fc/32 (fc/16 × 1/2) by the setting of <XEN> = 1, <XTEN> =

0, <SYSCK>

= 0, and <GEAR2:0> = 100 upon resetting.

For example, fSYS is set to 0.625 MHz by resetting in the case where the 20 MHz

oscillator is connected to the X1 and X2 pins.

The high frequency (fc) and low frequency (fs) clock signals can be easily obtained by

connecting a resonator to the X1 and X2, XT1 and XT2 pins, respectively. Clock input from

an external oscillator is also possible.

The XT1 and XT2 pins can also function as ports 96 and 97. Therefore in the case of

single clock mode, the XT1 and XT2 pins can be used as I/O port pins.

Figure 3.3.4 Examples of Resonator Connection

Note 1: Note on using the low-frequency oscillation circuit.

In connecting the low-frequency resonator to ports 96 and 97, it is necessary to make the

following settings to reduce the power consumption.

(Connecting with resonators) P9CR<P96C, P97C>

= 11, P9<P96:97> = 00

(Connecting with oscillators) P9CR<P96C, P97C>

= 11, P9<P96:97> = 10

Note 2: Accurate adjustment of the oscillation frequency

The CLK pin output at 1/2 the system clock frequency (fSYS/2) is used to monitor the

oscillation clock.

With a system requiring adjustment of the oscillation frequency, an adjusting program must

be written.

Low-frequency clock

High-frequency clock

(b) External oscillator

(a) Crystal/ceramic

resonator

(b) External oscillator

74HCU04

* See application

circuit in chapter 5.

XT1

XT2

XT1

XT2

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