ST72734 datasheet(18/144 Pages) STMICROELECTRONICS

Teilenummer	ST72734

Bauteilbeschribung	8-BIT USB MCU FOR MONITORS, WITH UP TO 60K OTP, 1K RAM, ADC, TIMER, SYNC, TMU, PWM/BRM, H/W DDC & I2C

PDF	144 Pages

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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18 / 144 page

ST72774/ST727754/ST72734

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3 CLOCKS, RESET, INTERRUPTS & LOW POWER MODES

3.1 CLOCK SYSTEM

3.1.1 General Description

The MCU accepts either a crystal or an external

clock signal to drive the internal oscillator. The

internal clock (CPU CLK running at fCPU) is

derived from the external oscillator frequency

(fOSC), which is divided by 3. Depending on the

external quartz or clock frequency, a division factor

of 2 is optionally added to generate the 12 MHz

clock for the Sync Processor (clamp function) as

shown in Figure 7 and a second divider by 2 for the

6MHz USB clock.

The CPU clock is used also as clock for the

ST727x4 peripherals.

Note: In the Sync processor, an additional divider

by two is added in fast mode (same external timing

for this peripheral).

Figure 7. Clock divider chain

12 MHz

(Sync processor Clampout signal)

fCPU: 4 or 8 MHz

(CPU and peripherals)

OSC

12 MHz

FAST

24MHz

FAST=1 for 24MHZ oscillator

FAST=0 for 12 MHz oscillator

6 MHz

(USB)

12 MHz

24MHz

(TMU)

ST72734 Datenblatt(PDF) 18 Page - STMicroelectronics