EM6819 Datasheet, PDF (46/154 Pages) EM Microelectronic - MARIN SA – Sub-1V (0.6V) 8bit Flash MCU DC-DC Converter

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EM6819
9. OSCILLATOR AND CLOCKING STRUCTURE
The circuit contains
• 3 independent fully internal RC osillcators,
• 15Mhz factory pretrimmed
• 2Mhz factory pretrimmed
• 8kHz
• Either one of these external clock sources
o 32 KHz watch crystal oscillator (Crystal extern). Mapped on terminals PA4, PC4.
o 4 MHz Crystal or Resonator oscillator (Crystal or Resonator extern). Mapped on terminals PA4, PC4.
o External high or Low frequency clock input. Mapped on terminal PC4.
The oscillator source can be changed on the fly to always use the appropriate oscillator and clock setting according to
the desired speed for i.e high speed calculation or low speed controlling, and hence optimise the power consumption.
The circuit will always start-up on the 2MHz RC Oscillator.
All circuit internal clocks are derived from the above mentioned oscillators. These clock sources may be predivided
locally for optimum speed and power.
Figure 5; oscillator and clock selection architecture
Hi-Freq
trimmed
RC
Oscillators
RC_15M
RC_2M
Ck_15M
Ck_2M
SelCkHi[1:0]
Ck_Hi
PC4/OscOut
SelCkExt[1:0]
Ck_PC4
CkSwSelHi CkSwStsHi
LF
HF
Ck_Reson
Ck_Xtal32
PA4/OscIn
Resonator, 32kHz Crystal
Ext Clock
Ck_Ext
Clock
Synchro
switch
CkSwSelX
CkSwStsX
SelCkLo[1:0]
Ck_Lo
/4
Lo-Freq
RC
Oscillator
Ck_8k
RC_8k
CkSwSelLo
CkSwStsLo
SCWakeUp
Watchdog
Oscillators and Clock selection
SelCkCR[3:0]
/1/2/4/8
/16/32/64
/1/2/4/8
ReqCkHi/Lo
Ck_CR
CR816
CoolRISC
SelCkPR2[2:0]
/1/2/4/8
Pr2Ck[10:0]
Ck_Pr2 _Prescaler2
10 stages
Clock source for
ReqCkHi/Lo
SelCkPR1[2:0]
Timer, SPI, Debouncer
FreqOut
/1/2/4/8
Pr1Ck[15:0]
Ck_Pr1 Prescaler1
15 stages
ReqCkHi/Lo
Clock source for
RTC, Debouncer,Timer,
SPI, IRQ, FreqOut
/1/2/4/8
/16/32/64
Ck_ADC _{10 bit ADC}
The RC15Mhz Ck_15M and RC_2Mhz Ck_2M oscillators are factory pretrimmed, the RC_8kHz Ck_8k oscillator is the
only clock source for the watchdog and the sleep counter reset function, but can also be used as a very low system
clock. The RC_8kHz low frequency oscillator is not trimmed.
On the PA4 and PC4 an external 32 KHz Crystal Ck_Xtal or 4MHz Resonator/Crystal Ck_Reson oscillator can be
connected or one may have an external clock input Ck_PC4 on PC4. The selected output clock signal is Ck_Ext.
The Ck_Hi clock signal can come from the 15MHz RC, 2MHz RC, 4MHz Resontor/Crystal or the external high
frequency clock input on PC4.
The Ck_Lo clock signal can come from the 32 KHz Crystal oscillator, divided 32 KHz, 8 kHz RC or the low frequency
external clock on PC4; it is synchronized with the high frequency clock Ck_Hi if present. Ck_Lo clock synchronization
Copyright © 2009, EM Microelectronic-Marin SA
46
07 /09 – rev.D
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