ST72C171 datasheet(20/152 Pages) STMICROELECTRONICS

Part #	ST72C171

Description	8-BIT MCU with 8K FLASH, ADC, WDG, SPI, SCI, TIMERS SPGAs Software Programmable Gain Amplifiers, OP-AMP

PDF	152 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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ST72C171

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MULTIOSCILLATOR (MO) (Cont’d)

External RC Oscillator

This oscillator allows a low cost solution on the

main clock of the ST7 using only an external resis-

tor and an external capacitor (see Figure 15). The

selection of the external RC oscillator has to be

done by Option Byte.

The frequency of the external RC oscillator is fixed

by the resistor and the capacitor values:

The previous formula shows that in this MO mode,

the accuracy of the clock is directly linked to the

accuracy of the discrete components.

Figure 15. MO External RC

Internal RC Oscillator

The Internal RC oscillator mode is based on the

same principle as the External RC one including

the an on-chip resistor and capacitor. This mode is

the most cost effective one with the drawback of a

lower frequency accuracy. Its frequency is in the

range of several MHz.

In this mode, the two oscillator pins have to be tied

to ground as shown in Figure 16.

The selection of the internal RC oscillator has to

be done by Option Byte.

Figure 16. MO Internal RC

fOSC ~

REX . CEX

OSCin

OSCout

ST7

CEX

REX

OSCin

OSCout

ST7

ST72C171 Datasheet(PDF) 20 Page - STMicroelectronics