GMS81C1404 Datasheet, PDF (42/93 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C1404/GMS81C1408
11. 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 pin.
OSCILLATION ^fxin
CIRCUIT
CLOCK PULSE
GENERATOR
Internal system clock
STOP
WAKEUP
PRESCALER
÷1 ÷2 ÷4 ÷8 ÷16 ÷32 ÷64 ÷128 ÷256 ÷512 ÷1024 ÷2048
Peripheral clock
Figure 11-1 Block Diagram of Clock Pulse Generator
11.1 Oscillation Circuit
X_IN and X_OUT 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 11-2 .
Xout
C1
R1
C2
Xin
Vss
should consult the crystal manufacturer for appropriate
values of external components.
OPEN
Xout
External
Clock
Xin
Source
Vss
Recommended: C1, C2 = 30pF±10pF for Crystals
R1 = 1MΩ
Figure 11-2 Oscillator Connections
To drive the device from an external clock source, Xout
should be left unconnected while Xin is driven as shown in
Figure 11-3 . 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.
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
Figure 11-3 External Clock Connections
Note: When using a system clock oscillator, carry out wir-
ing in the broken line area in Figure 11-2 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
oscillator capacitor to that of VSS. Do not ground to
any ground pattern where high current is present.
- Do not fetch signals from the oscillator.
40
June. 2001 Ver 1.2