IBM EM78M611E 8.6 Reset , 8.7 Saving Power Mode

EM78M611E

Universal Serial Bus Series Microcontroller

Product Specification (V1.11) 04.20.2007

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(This specification is subject to change without further notice)

EM78M611E supports one device address and three endpoints, EP0 for control

endpoint, EP1 and EP2 for interrupt endpoint. Sending data to USB host in

EM78M611E is very easy. Just write data into EP’s FIFO, then set flag, and the UDC

will handle the rest. It will then confirm that the USB host has received the correct data

from EM78M611E.

8.6 Reset

The EM78M611E provides three types of reset: ( 1) Power-on Reset, (2) Watchdog

Reset, and (3) USB Reset.

Power-on Reset occurs when the device is attached to power and a reset signal is

initiated. The signal will last until the MCU becomes stable. After a Power-on Reset,

the MCU enters into the following predetermined states (see below), and then, it is

ready to execute the program.

a. The program counter is cleared.

b. The TCC timer and Watchdog timer are cleared.

c. Special registers and Special Control registers are all set to their initial values.

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.

When the UDC detects a USB Reset signal on the USB Bus, an MCU interrupt occurs,

after which it proceeds 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.

8.7 Saving Power Mode

The EM78M611E provides two options of power-saving modes for energy conservation,

i.e., Power Down mode and Dual clock mode.

The EM78M611E 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 a Watchdog reset occurs

or when an input port state changes.

If the MCU wakes up when I/O port status changes, the direction of the I/O port should

be set at input direction, and then read the state of port. For example: