ST7LITE20 datasheet(24/131 Pages) STMICROELECTRONICS

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ST7LITE2

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PHASE LOCKED LOOP (Cont’d)

Figure 12. PLL Output Frequency Timing

Diagram

When the PLL is started, after reset or wakeup

from Halt mode or AWUFH mode, it outputs the

clock after a delay of tSTARTUP.

When the PLL output signal reaches the operating

frequency, the LOCKED bit in the SICSCR register

is set. Full PLL accuracy (ACCPLL) is reached after

a stabilization time of tSTAB (see Figure 12 and

13.3.4 Internal RC Oscillator and PLL)

Refer to section 7.6.4 on page 33 for a description

of the LOCKED bit in the SICSR register.

7.3 REGISTER DESCRIPTION

MAIN CLOCK CONTROL/STATUS REGISTER

(MCCSR)

Read / Write

Reset Value: 0000 0000 (00h)

Bits 7:2 = Reserved, must be kept cleared.

Bit 1 = MCO

Main Clock Out enable

This bit is read/write by software and cleared by

hardware after a reset. This bit allows to enable

the MCO output clock.

0: MCO clock disabled, I/O port free for general

purpose I/O.

1: MCO clock enabled.

Bit 0 = SMS

Slow Mode select

This bit is read/write by software and cleared by

hardware after a reset. This bit selects the input

clock fOSC or fOSC/32.

0: Normal mode (fCPU = fOSC

1: Slow mode (fCPU = fOSC/32)

RC CONTROL REGISTER (RCCR)

Read / Write

Reset Value: 1111 1111 (FFh)

Bits 7:0 = CR[7:0]

RC Oscillator Frequency Ad-

justment Bits

These bits must be written immediately after reset

to adjust the RC oscillator frequency and to obtain

an accuracy of 1%. The application can store the

correct value for each voltage range in EEPROM

and write it to this register at start-up.

00h = maximum available frequency

FFh = lowest available frequency

Note: To tune the oscillator, write a series of differ-

ent values in the register until the correct frequen-

cy is reached. The fastest method is to use a di-

chotomy starting with 80h.

4/8 x

freq.

LOCKED bit set

tSTAB

tLOCK

input

tSTARTUP

0000

MCO

SMS

CR70 CR60 CR50 CR40 CR30 CR20 CR10 CR0

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