參數(shù)資料
型號: ST72E85A5G0
廠商: STMICROELECTRONICS
元件分類: 微控制器/微處理器
英文描述: 8-BIT, UVPROM, 4.332 MHz, MICROCONTROLLER, CQFP80
封裝: WINDOWED, CERAMIC, QFP- 80
文件頁數(shù): 25/117頁
文件大?。?/td> 748K
代理商: ST72E85A5G0
15/117
ST7285C
3 CLOCKS, RESET, INTERRUPTS & POWER SAVING MODES
3.1 CLOCK SYSTEM
3.1.1 General Description
The MCU accepts either a Crystal or Ceramic res-
onator, or an external clock signal to drive the in-
ternal oscillator. The internal clock (CPU CLK run-
ning at fCPU) is derived from the external oscillator
frequency (fOSC). The external Oscillator clock is
first divided by 2, and an additional division factor
of 2, 4, 8, or 16 can be applied, in Slow Mode, to
reduce the frequency of the CPU clock (see
note 1); this clock signal is also routed to the on-
chip peripherals. The CPU clock signal consists of
a square wave with a duty cycle of 50%.
Figure 4. External Clock Source Connections
Figure 5. Equivalent Crystal Circuit
3.1.2 Crystal Resonator
The internal oscillator is designed to operate with
an AT-cut parallel resonant quartz crystal resona-
tor in the frequency range specified for fosc.The
circuit shown in Figure 6 is recommended when
using a crystal, and Table 2 lists the recommend-
ed capacitance and feedback resistance values.
The crystal and associated components should be
mounted as close as possible to the input pins in
order to minimize output distortion and start-up
stabilisation time.
Use of an external CMOS oscillator is recom-
mended when crystals outside the specified fre-
quency ranges are to be used.
Figure 6. Crystal/Ceramic Resonator
Figure 7. Clock Prescaler Block Diagram
Note 1: Additional division factor of CPU clock is only available on L5/L6.
OSCin
OSCout
EXTERN AL
CLOCK
NC
OSCin
OSCout
RS
L1
C1
C0
OSCin
OSCout
COSCin
COSCout
RP
OSCin
OSCout
COSCin
COSCout
RP
%2
%2,4,8,16
CPUCLK
to CPU and
Peripherals
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