TMP93CS44 datasheet(19/224 Pages) TOSHIBA

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TMP93CS44/S45

2004-02-10

93CS44-17

3.3.1

System Clock Controller

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

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

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

controls enable/disable each oscillator, SYSCR1<GEAR2:0> changes high-frequency clock

gear to either 1, 2, 4, 8 or 16 (fc, fc/2, fc/4, fc/8 or fc/16), and 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) because of <XEN> = “1”, <XTEN> = “0”,

<SYSCK>

= “0”, <GEAR2:0> = “100” by resetting. For example, fSYS is set to 0.625 MHz by

resetting the case of 20 MHz oscillator is connected to X1, X2 pins.

The high-frequency (fc) and low-frequency (fs) clocks can be easily obtained by connecting

a resonator to the X1/X2, XT1/XT2 pins, respectively. Clock input from an external

oscillator is also possible.

The XT1, XT2 pins have also port 66, 67 function. Therefore the case of single clock mode,

the XT1, 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 66 and 67, it is necessary to make the

following settings to reduce the power consumption.

(Connecting with resonators)

P6CR<P66C:67C> = “11”, P6<P66:67> = “00”

(Connecting with oscillators)

P6CR<P66C:67C>

= “11”, P6<P66:67> = “10”

Note 2: Accurate adjustment of the oscillation frequency.

The CLK pin outputs 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.

74HCU04

(a) Crystal/ceramic

resonator

(b) External oscillator

High-frequency clock

XT1

XT2

XT1

XT2

(d) External oscillator

Low-frequency clock

(Open)

Refer to chapter

5 “Application

Circuit.”

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