EM78M612
Universal Serial Bus Microcontroller Series
8.5.2 WatchDog Reset
When the WatchDog timer overflows, it causes the WatchDog to reset. After it resets, the
program is executed from the beginning and some registers will be reset. The UDC however,
remains unaffected.
8.5.3 USB Reset
When UDC detects a USB Reset signal on USB Bus, it interrupts the MCU, then proceed to
perform the specified process that follows.
8.6 Power Saving Mode
The EM78M612 provides two options of power saving modes for energy conservation, i.e.,
Power Down mode, and Dual Clock mode.
8.6.1 Power Down Mode
The EM78M612 enters into Power Down mode by clearing the RUN register (IOCE[4]).
During this mode, the oscillator is turned off and the MCU goes to sleep. It will wake up
when signal from USB host is resumed, or when the WatchDog resets, or the input port state
changes.
If the MCU wakes up when I/O port status changes, I/O port direction should be set at input,
then the port state is read. For example:
:
// Set the Port 6 to input port
MOV
IOW
A , 0XFF
PORT6
// Read the state of Port 6
MOV PORT6, PORT6
// Clear the RUN bit
IOR
AND
IOW
:
0XE
A , 0B11101111
0XE
:
If the MCU is awaken by a USB Resume signal, the next instruction will be executed, and
one flag, RC[3] will be set to 1.
8.6.2 Dual Clock Mode
The EM78M612 has one internal oscillator for power saving application. Clearing the Bit
IOCE [7] will enable the low frequency oscillator. At the same time, the external oscillator will
be turned off. Then the MCU will run under very low frequency to conserve power. Four
types of frequency are available for selection in setting Bits IOCA [6, 7].
This specification may change without further notice.
2004/4/28 V1.1
28
ELAN [ ELAN MICROELECTRONICS CORP ]
