TMP93CS44 Datasheet, PDF (19/224 Pages) Toshiba Semiconductor – CMOS 16-Bit Microcontroller

TMP93CS44/S45
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.
High-frequency clock
X1
X2
X1
X2
Low-frequency clock
XT1
XT2
XT1
XT2
(Open)
(a) Crystal/ceramic
resonator
74HCU04
Refer to chapter
5 “Application
Circuit.”
(b) External oscillator
(c) Crystal resonator
(d) External oscillator
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 (f_SYS/2) is used to monitor the oscillation
clock. With a system requiring adjustment of the oscillation frequency, an adjusting program
must be written.
93CS44-17
2004-02-10