EM6812 Datasheet, PDF (29/81 Pages) EM Microelectronic - MARIN SA – Ultra Low Power 8-bit FLASH Microcontroller

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EM6812
8.6.1 Prescaler2 (10 stages)
The prescaler 2 has two selectable clock sources possible. By default it is running on RC oscillator.
• Pr2CkSel = ‘0’: LF clock domain (F1: Xtal oscillator or external clock).
• Pr2CkSel = ‘1’: HF clock domain after pre-division (F2) divided by 2 (RC oscillator or external clock) F2/2.
Pr2CkSource is the clock source of the prescaler2. 10 different clocks get out from the prescaler2; Pr2Ck[9:0].
The shaded values are selected for prescaler1 clock input in case of autoselect and no active low frequency.
All clock duty cyles are 50% expecpt for the Pr2CkSource which is 25% high if issued from the high frequency input clock.
Table 20. Prescaler2 output frequencies when running on HF clock domain (CkPeri_High_Freq)
RC Oscillator
10MHz 10MHz 10MHz 10MHz 1MHz
1MHz
Pre-Division by
1
2
4
8
1
2
Pr2CkSource
(Duty: 25% high)
F2/2
5MHz
F2/2
F2/2
F2/2
F2/2
2.5MHz 1.25MHz 625kHz _500kHz
F2/2
250kHz
Pr2Ck[9] Pr2CkSource / 2
2.5MHz 1.25MHz 625kHz 313kHz 250kHz 125kHz
Pr2Ck[8] Pr2CkSource / 4
1.25MHz 625kHz 313kHz 156kHz 125kHz 62.5kHz
Pr2Ck[7] Pr2CkSource / 8
625kHz 313kHz 156kHz 78kHz 62.5kHz 31.3kHz
Pr2Ck[6] Pr2CkSource / 16
313kHz 156kHz 78kHz 39kHz 31.3kHz 15.6kHz
Pr2Ck[5] Pr2CkSource / 32
156kHz 78kHz 39kHz 20kHz 15.6kHz 7.8kHz
Pr2Ck[4] Pr2CkSource / 64
78kHz 39kHz 20kHz 10kHz 7.8kHz 3.9kHz
Pr2Ck[3] Pr2CkSource / 128 39kHz 20kHz 10kHz
5kHz
3.9kHz 2.0kHz
Pr2Ck[2] Pr2CkSource / 256 20kHz 10kHz
5kHz 2.4kHz 2.0kHz 1.0kHz
Pr2Ck[1] Pr2CkSource / 512 10kHz
5kHz
2.4kHz 1.2kHz 1.0kHz 500Hz
Pr2Ck[0] Pr2CkSource / 1024 5kHz 2.4kHz 1.2kHz 610Hz 500Hz 250Hz
1MHz
4
F2/2
125kHz
62.5kHz
31.3kHz
15.6kHz
7.8kHz
3.9kHz
2.0kHz
1.0kHz
500Hz
250Hz
125Hz
1MHz
8
F2/2
62.5kHz
31.3kHz
15.6kHz
7.8kHz
3.9kHz
2.0kHz
1.0kHz
500Hz
250Hz
125Hz
62Hz
The prescaler2 clock values, 8 MSB's, Pr2CkStatus[7:0] can be read in register RegPr2Status. These 8 most significative
bits can be cleared by a simple write operation of any value to the RegPr2Status register.
The Pr2Ck sources are used as input clock sources for several other peripheries (SPI, Timers, Prescaler1, etc). Clearing
the 8 MSB’s may therefore influence the proper operation of these peripheries.
Table 21. Prescaler2 output frequencies when running on LF clock domain (CkPeri_Low_Freq)
Signal name
Division
Presacler 2 output frequency
In case of XTAL 32kHz as active
low frequency clock
Pr2CkSource
Pr2CkSource / 1
32768Hz
Pr2Ck[9]
Pr2CkSource / 2
16384Hz
Pr2Ck[8]
Pr2CkSource / 4
8192Hz
Pr2Ck[7]
Pr2CkSource / 8
4096Hz
Pr2Ck[6]
Pr2CkSource / 16
2048Hz
Pr2Ck[5]
Pr2CkSource / 32
1024Hz
Pr2Ck[4]
Pr2CkSource / 64
512Hz
Pr2Ck[3]
Pr2CkSource / 128
256Hz
Pr2Ck[2]
Pr2CkSource / 256
128Hz
Pr2Ck[1]
Pr2CkSource / 512
64Hz
Pr2Ck[0]
Pr2CkSource / 1024
32Hz
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