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EM6819 Datasheet(PDF) 46 Page - EM Microelectronic - MARIN SA |
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EM6819 Datasheet(HTML) 46 Page - EM Microelectronic - MARIN SA |
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46 / 154 page  R EM6819 Copyright © 2009, EM Microelectronic-Marin SA 07 /09 – rev.D 46 www.emmicroelectronic.com 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 PC4/OscOut RC_15M RC_2M LF HF Ck_Ext Ck_Reson Ck_Xtal32 Ck_15M Ck_2M RC_8k Ck_8k PA4/OscIn Ck_Hi Ck_Lo Ck_CR Ck_Pr2 Ck_Pr1 /4 RTC, Debouncer,Timer, SPI, IRQ, FreqOut CoolRISC Timer, SPI, Debouncer FreqOut Prescaler2 10 stages CR816 Prescaler1 15 stages Pr1Ck[15:0] Pr2Ck[10:0] Watchdog /1/2/4/8 /1/2/4/8 /1/2/4/8 /16/32/64 /1/2/4/8 SelCkExt[1:0] SelCkHi[1:0] SelCkLo[1:0] SelCkCR[3:0] SelCkPR2[2:0] SelCkPR1[2:0] Oscillators and Clock selection Resonator, 32kHz Crystal Ext Clock Hi-Freq trimmed RC Oscillators Lo-Freq RC Oscillator /1/2/4/8 /16/32/64 10 bit ADC Clock source for Clock source for Ck_ADC SCWakeUp Ck_PC4 Clock Synchro switch CkSwSelLo CkSwStsLo CkSwSelX CkSwStsX CkSwSelHi CkSwStsHi ReqCkHi/Lo ReqCkHi/Lo ReqCkHi/Lo 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 |
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