EM6812F2TP24B datasheet(30/81 Pages) EMMICRO

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EM6812

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8.6.2

Prescaler1 (15 stages)

•

8 clock input selections from Xtal or Prescaler2 clocks.

•

RTC real time clock function in case of 32kHz Xtal input.

•

‘Autoselect’ close to 32kHz input clock selection from prescaler2 in case of no Xtal. The autoselection is based on the

RC oscillator settings (FreqRange and RCDiv) and switched on with bit AutoSel in register RegPrCkSel. In case of an

active low frequency clock selection (Xtal or external low frequency enabled) the autoselect will select the low

frequency input F1 as the prescaler clock source. The clock switching is based on the scheme as shown in Figure 17.

Synchronous Clock switching.

Table 22. Table of the Prescaler1 automatic clock selection from prescaler2. (AutoSel = ‘1’, Pr2CkSel =’1’)

FreqRange

RC = 10 MHz

RC = 1MHz

RCDiv

Pr2CkSource

5MHz

2.5MHz

1.25MHz

625kHz

500kHz

250kHz

125kHz

62.5kHz

Pr2Ck[9:0] selected bit

[3]

[4]

[5]

[6]

[7]

[8]

[9]

Pr1CkSource, AutoSel

39.1kHz

31.3kHz

31.3 kHz

The low frequency clock gets automatic selected as Pr2CkSource in case of Autosel = ‘1’ and Pr2CkSel = ‘0’.

The prescaler1 clock values, 8 MSB's, Pr1CkStatus[7:0] can be read in register RegPr1Status. These 8 most significative

bits can be cleared by a simple write operation of any value to the RegPr1Status register.

The Pr1Ck sources are used as input clock sources for several other peripheries (SPI, Timer, etc). Clearing the 8 MSB’s

may therefore influence the proper operation of these peripheries.

It is also possible to select a specific prescaler1 input clock source by setting AutoSel=‘0’. The selection is done with bits

Pr1CkSel

[2:0] in register RegPrescCkSel.

Table 23. Prescaler1 clock selection, non-automatic mode. (AutoSel = ‘0’)

Pr1CkSel[2:0]

Clock selected in case of

Pr2CkSel=’1’ (high freq.)

on RC Oscillator

Clock selected in case of

Pr2CkSel=’0’ (low freq.)

with 32kHz Crystal

000

Low frequency clock domain F1

(Xtal or ExtLFck)

Low frequency clock domain F1

(Xtal or ExtLFck)

001 (default)

Prc2Ck[3], refer to Table 20

Prc2Ck[3] = 16384Hz

010

Prc2Ck[4], refer to Table 20

Prc2Ck[4] = 8192Hz

011

Prc2Ck[5], refer to Table 20

Prc2Ck[5] = 4096Hz

100

Prc2Ck[6], refer to Table 20

Prc2Ck[6] = 2048Hz

101

Prc2Ck[7], refer to Table 20

Prc2Ck[7] = 1024Hz

110

Prc2Ck[8], refer to Table 20

Prc2Ck[8] = 512Hz

111

Prc2Ck[9], refer to Table 20

Prc2Ck[9] = 256Hz

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