HMS87C1808B Datasheet, PDF (45/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
10. CLOCK GENERATOR
The clock generator produces the basic clock pulses which pro-
vide the system clock to be supplied to the CPU and peripheral
hardware. The main system clock oscillator oscillates with a crys-
tal 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 10-1 Block Diagram of Clock Pulse Generator
10.1 Oscillation Circuit
X_IN and X_OUT are the input and output, respectively, a inverting
amplifier which can be set for use as an on-chip oscillator, as
shown in Figure 10-2 .
nents.
OPEN
Xout
Xout
C1
C2
Xin
Vss
Recommended: C1, C2 = 30pF±10pF for Crystals
Figure 10-2 Oscillator Connections
To drive the device from an external clock source, Xout should
be left unconnected while Xin is driven as shown in Figure 10-3
. 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 ceramic
resonator or crystal oscillator. Since each crystal and ceramic res-
onator have their own characteristics, the user should consult the
crystal manufacturer for appropriate values of external compo-
External
Clock
Xin
Source
Vss
Figure 10-3 External Clock Connections
Note: When using a system clock oscillator, carry out wir-
ing in the broken line area in Figure 10-2 to prevent any ef-
fects from wiring capacities.
- Minimize the wiring length.
- Do not allow wiring to intersect with other signal conduc-
tors.
- 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 pat-
tern where high current is present.
- Do not fetch signals from the oscillator.
In addition, the HMS87C1X04B/08B/16B has an ability for the
external RC oscillated operation. It offers additional cost savings
for timing insensitive applications. The RC oscillator frequency
is a function of the supply voltage, the external resistor (R_EXT)
and capacitor (C_EXT) values, and the operating temperature.
SEP. 2004 Ver 1.03
41