EM77930 Datasheet, PDF (103/114 Pages) ELAN Microelectronics Corp – USB + BB Controller

EM77930
USB+BB Controller
16 Low-Power Mode
16.1 Introduction
The EM77930 has two power-saving modes, green mode and sleep mode. Figure 16
shows the mode change diagram.
Power On
Normal
Key Wake up
WDTC[7].Green=0
SLEP INST.
1. WDTC[7].Green=1
2. WDT Time out
3. /Reset
Green
SLEP INST.
1. Key Wake-up
2. WDT Time out
3. /Reset
Sleep
Fig. 16 Three Mode State
16.2 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 will be turned off. The MCU and all the
peripherals are driven by the external RC oscillator - IRC.
Once RF peripheral is functional and then switched into green mode, the clock source
for all the other peripherals, except PLL, will be provided by IRC. PLL will keep running
as RF circuit’s clock source.
Product Specification (V1.0) 08.20.2007
• 95
(This specification is subject to change without further notice)