st52f510 STMicroelectronics, st52f510 Datasheet - Page 44

• Manufacturer Part Number: st52f510
• Description: 8-bit Intelligent Controller Unit Icu Two Timer/pwms, Adc, I2c, Spi, Sci
• Manufacturer: STMicroelectronics

ST52F510/F513/F514
6 CLOCK, RESET & POWER SAVING MODES
6.1 Clock
The
module generates the internal clock for the internal
Control Unit, ALU and on-chip peripherals. The
Clock is designed to require a minimum of external
components.
ST52F510/F513/F514 devices supply the internal
oscillator in four clock modes:
The device always starts in internal clock mode,
excluding any external clock source. After the
start-up phase the clock is configured according to
the user definition programmed in the Option Byte
0 (OSC_CR). The internal clock generator can
supply an internal clock signal with a fixed
frequency of 10 MHz ± 1%, without the need for
external components. In order to obtain the
maximum accuracy, the frequency can be
calibrated by configuring the related Option byte 2
(OSC_SET).
The external oscillator mode uses a quartz crystal
or a ceramic resonator connected to OSCin and
OSCout as illustrated in Figure 6.1. This figure also
illustrates the connection of an external clock.
The
generates an internal clock signal with the same
period and phase as the OSCIN input pin. The
maximum frequency allowed is 24 MHz.
When the external oscillator is used, the loop gain
can be adapted to the various frequencies values
by configuring the three bits of the Option Byte 1
CLK_SET (see Register Decription, Table 6.2).
When an external clock is used, it must be
connected to the pin OSCIN while OSCOUT can
Figure 6.1 Oscillator Connections
44/106
External oscillator
External clock
External RC oscillator
Internal clock
ST52F510/F513/F514
ST52F510/F513/F514
Cl1
10pF
OSCin
CRYSTAL CLOCK
ST FIVE
OSCout
Clock
oscillator
Cl2
10pF
Generator
circuit
OSCin
CLOCK
INPUT
EXTERNAL CLOCK
ST FIVE
be floating. In this case, Option Byte 1 bits must be
written with 0 (000).
The crystal oscillator start-up time is a function of
many variables: crystal parameters (especially
R
parameters, environment temperature and supply
voltage.
The
connections must be as short as possible. Typical
values for CL1, CL2 are 10pF for a 20 MHz crystal.
The clock signal can also be generated by an
external RC circuit offering additional cost savings.
Figure 6.1 illustrates the possible connections.
Frequency is a function of resistor, capacitance,
supply voltage and operating temperature; some
indicative values when Vdd=5V and T=25°, ar e
shown in Table 6.1.
The clock signal generates two internal clock
signals: one for the CPU and one for the
peripherals. The CPU clock frequency can be
reduced, in order to decrease current consuption,
by setting the CPU_CLK Configuration Register 46
(02Eh). The CPU clock can be reduced up to 64
times (see Register Description).
Table 6.1 RC Oscillator indicative frequencies
s
),
100 pF
C (pF)
20 pF
OSCout
crystal
oscillator
or
100K
100K
R( )
9.5K
10K
20K
50K
10K
20K
50K
load
Vdd
R
ceramic
OSCin
RC CIRCUIT CLOCK
capacitance
Vss
f
ST FIVE
osc
C
5000
4870
3000
1360
1720
724
926
424
248
leads
(KHz)
OSCout
and
Variation
(CL),
11.2%
6.6%
7.1%
5.3%
3.3%
2.8%
7.5%
15%
8%
circuit
IC