GMS81C1102 / GMS81C1202
14. CLOCK GENERATOR
The clock generator produces the basic clock pulses which
provide the system clock to be supplied to the CPU and pe-
ripheral hardware. The main system clock oscillator oscillates
with a crystal resonator or a ceramic resonator connected to the
Xin and Xout pins. External clocks can be input to the main
system clock oscillator. In this case, input a clock signal to
the Xin pin and open the Xout pinꢀ
fxin
OSCILLATION
CIRCUIT
CLOCK PULSE
GENERATOR
Internal system clock
PRESCALER
STOP
WAKEUP
÷1
÷2
÷4
÷8
÷16
÷32
÷64
÷128 ÷256 ÷512 ÷1024 ÷2048
Peripheral clock
Figure 14-1 Block Diagram of Clock Pulse Generator
14.1 Oscillation Circuit
XIN and XOUT are the input and output, respectively, a in-
verting amplifier which can be set for use as an on-chip os-
cillator, as shown in Figure 14-2 .
ings for timing insensitive applications. The RC
oscillator frequency is a function of the supply voltage, the
external resistor (Rext) and capacitor (Cext) values, and
the operating temperature.
Xout
The user needs to take into account variation due to toler-
ance of external R and C components used. Figure 14-4
shows how the RC combination is connected to the
GMS81C1202.
C1
C2
R1
Xin
Vss
OPEN
Xout
Recommended: C1, C2 = 30pF±10pF for Crystals
R1 = 1MΩ
External
Clock
Xin
Source
Figure 14-2 Oscillator Connections
Vss
To drive the device from an external clock source, Xout
should be left unconnected while Xin is driven as shown in
Figure 14-3. There are no requirements on the duty cycle
of the external clock signal, since the input to the internal
clocking circuitry is through a divide-by-two flip-flop, but
minimum and maximum high and low times specified on
the data sheet must be observed.
Figure 14-3 External Clock Connections
Note: When using a system clock oscillator, carry out wir-
ing in the broken line area in Figure 14-2 to prevent
any effects from wiring capacities.
- Minimize the wiring length.
- Do not allow wiring to intersect with other signal
conductors.
- Do not allow wiring to come near changing high
current.
- Set the potential of the grounding position of the
Oscillation circuit is designed to be used either with a ce-
ramic resonator or crystal oscillator. Since each crystal and
ceramic resonator have their own characteristics, the user
should consult the crystal manufacturer for appropriate
values of external components
SS
oscillator capacitor to that of V . Do not ground to
any ground pattern where high current is present.
- Do not fetch signals from the oscillator.
In addition, the GMS81C1202 has an ability for the exter-
nal RC oscillated operation. It offers additional cost sav-
Jan. 2002 ver 2.0
41
HYNIX [ HYNIX SEMICONDUCTOR ]
