EM77950 datasheet(95/102 Pages) EMC

95 / 102 page

EM77950

BB Controller

Product Specification (V1.0) 10.09.2007

• 87

(This specification is subject to change without further notice)

17.2

Green Mode

The “GREEN” bit of WDTC [7] register is the only control bit used for mode switching

between normal mode and green mode. Its initial value is “0”, normal mode. When

“GREEN” bit is written with a 1, the MCU will switch to green mode from normal mode.

In contrast, the MCU will go back to normal mode when the “GREEN” bit is written from

1 to 0. During green mode, the main oscillator and PLL will be turned off. The MCU

and all the peripherals are driven by the internal RC oscillator - IRC.

Once BB peripheral is functional and then switched into green mode, the clock source

of all other peripherals, except PLL, will be provided by IRC. PLL will keep running as

BB circuit’s clock source.

17.3

Sleep Mode

The execution of “SLEP” instruction will turn the whole chip into Sleep mode. The main

clock will be shut down. The IRC oscillator is halted also if the watchdog function is

disabled. All registers, memory and I/O port remain in their previous states during

sleep mode. The overflow of the watchdog timer driven by IRC will generate a reset to

resume normal operation. Key Wake up (KWU) interrupt and /RESET pin are other

methods to exit sleep mode. It is essential to wait for stable Oscillation start-up time

before normal operation. The stabilizing time is SST.

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