EM783 datasheet(21/58 Pages) NXP

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EM783

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Product data sheet

Rev. 2 — 17 January 2014

21 of 58

NXP Semiconductors

EM783

Energy metering IC; 32 kB flash, 8 kB SRAM, 4 kB EEPROM

7.18.1.1

Internal RC Oscillator (IRC)

The IRC may be used as the clock source for the WWDT, and/or as the clock that drives

the PLL and subsequently the CPU. The nominal IRC frequency is 12 MHz. The IRC is

trimmed to 1 % accuracy over the entire voltage and temperature range.

The IRC can be used as a clock source for the CPU with or without using the PLL. The

IRC frequency can be boosted to a higher frequency, up to the maximum CPU operating

frequency, by the system PLL.

Upon power-up or any chip reset, the EM783 use the IRC as the clock source. Software

may later switch to one of the other available clock sources.

7.18.1.2

Crystal Oscillator (SysOsc)

The crystal oscillator can be used as the clock source for the CPU, with or without using

the PLL.

The SysOsc operates at frequencies of 1 MHz to 25 MHz. This frequency can be boosted

to a higher frequency, up to the maximum CPU operating frequency, by the system PLL.

Fig 4.

EM783 clock generation block diagram

aaa-009615

SYSTEM PLL

IRC

SysOsc

WDOsc

IRC

LFOsc

MAINCLKSEL

(main clock select)

SYSPLLCLKSEL

(system PLL clock select)

SYSTEM CLOCK

DIVIDER

system

SYSCLKCTRL[1:18]

memories

and peripherals

SSP0 PERIPHERAL

CLOCK DIVIDER

SSP0

USART PERIPHERAL

CLOCK DIVIDER

USART

WWDT CLOCK

DIVIDER

WWDT

WDCLKSEL

LFOsc

IRC

SysOsc

CLKOUT PIN CLOCK

DIVIDER

CLKOUT pin

CLKOUTUEN

(CLKOUT update enable)

main clock

system clock

IRC

CLKIN

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