st52t430 STMicroelectronics, st52t430 Datasheet - Page 32

• Manufacturer Part Number: st52t430
• Description: 8-bit Intelligent Controller Unit Icu Three Timer/pwms, Adc, Sci
• Manufacturer: STMicroelectronics

5 CLOCK, RESET & POWER SAVING MODE
5.1 System Clock
The ST52x430 Clock Generator module generates
the internal clock for the internal Control Unit, ALU
and on-chip peripherals and it is designed to
require
components.
The ST52x430 oscillator circuit generates an
internal clock signal with the same period and
phase as that of the OSCin input pin. The
maximum frequency allowed is 20 Mhz.
Note: When the SCI peripheral is used only a 5,
10, or 20 MHz system clock must be used.
The system clock may be generated by using
either a quartz crystal, ceramic resonator or an
external clock.
The different methods of the clock generator are
illustrated in Figure 5.1.
When an external clock is used, it must be
connected on the OSCin pin, while OSCout can be
floating.
The crystal oscillator start-up time is a function of
many variables: crystal parameters (especially
R
parameters, environment temperature, supply
voltage.
Figure 5.1 Oscillator Connections
32/88
s
),
oscillator
Cl1
a
10pF
OSCin
minimum
CRYSTAL CLOCK
load
ST52X430
capacitance
number
OSCout
of
Cl2
10pF
(CL),
external
IC
Note: The crystal or ceramic leads and circuit
connections must be as short as possible. Typical
values for CL1, CL2 are 10pF for a 20 MHz crystal.
5.2 RESET
There are two Reset sources:
- RESET pin (external source.)
- WATCHDOG (internal source)
When a Reset event happens, the user program
restarts from the beginning.
The Reset pin is an input. An internal reset does
not affect this pin.
A Reset signal originated by external sources is
recognized instantaneously. The RESET pin may
be used to ensure V
the MCU can operate correctly before the user
program runs. In working mode Reset must be set
to ‘1’ (see Table 2.1).
5.3 Power Saving Mode
There are two Power Saving modes: WAIT and
HALT mode. These conditions may be entered
using the WAIT or HALT instructions.
5.3.1 Wait Mode
Wait mode places the MCU in low power
consumption by stopping the CPU. All peripherals
OSCin
CLOCK
INPUT
EXTERNAL CLOCK
ST52X430
DD
has risen to a point where
OSCout