EMC EM78612 - Manual (Page 27)

EM78612
Universal Serial Bus Microcontroller
Product Specification (V1.0) 03.22.2006 •••• 25
(This specification is subject to change without further notice)
C. Special registers and Special Control registers are all set to initial value.
The MCU also has a low voltage detector that detects low output power condition.
Whenever the output voltage of the 3.3V regulator decreases to below 2.2V, a reset
signal is set off.
7.5.2 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.
7.5.3 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. After a USB device is attached to
the USB port, it cannot respond to any bus transactions until it receives a USB Reset
signal from the bus.
7.6 Power Saving Mode
The EM78612 provides two options of power saving modes for energy conservation,
i.e., Power Down mode, and Dual Clock mode.
7.6.1 Power Down Mode
The EM78612 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, the direction of I/O port direction
should be set at input direction, then read the state of port. For example:
// Set the Port 6 to input port
MOV A,@0XFF
IOW PORT6
// Read the state of Port 6
MOV PORT6,PORT6
// Clear the RUN bit
IOR 0X0E
AND A,@0B11101111
IOW 0X0E