IBM EM78P447N manual RESET and Wake-up, Reset

EM78P447N

8-Bit Microcontroller with OTP ROM

4.5 RESET and Wake-up

4.5.1 RESET

A RESET is initiated by one of the following events-

(1)Power on reset, or

(2)/RESET pin input “low”, or

(3)WDT timeout. (if enabled)

The device is kept in a RESET condition for a period of approx. 18ms3 (one oscillator start-up timer period) after the reset is detected. Once the RESET occurs, the following functions are performed (refer to Fig.8).

The oscillator starts or is running

The Program Counter (R2) is set to all "1".

When power is switched on, bits 5~6 of R3 and the upper 2 bits of R4 are cleared.

All I/O port pins are configured as input mode (high-impedance state).

The Watchdog timer and prescaler are cleared.

Upon power on, the bits 5~6 of R3 are cleared.

Upon power on, the upper 2 bits of R4 are cleared.

The bits of CONT register are set to all "1" except bit 6 (INT flag).

IOCB register is set to ”1” (disable P60 ~ P67 wake-up function).

Bits 3 and 6 of IOCE register are cleared, and Bits 0, 4, and 5 are set to "1".

Bits 0 and 3 of R3F register and Bits 0 and 3 of IOCF registers are cleared.

The sleep (power down) mode is asserted by executing the “SLEP” instruction. While entering sleep mode, WDT (if enabled) is cleared but keeps on running. The controller can be awakened by-

(1)External reset input on /RESET pin;

(2)WDT time-out (if enabled)

The above two cases will cause the controller EM78P447N to reset. The T and P flags of R3 can be used to determine the source of the reset (wake-up).

In addition to the basic SLEEP1 MODE, EM78P447N has another sleep mode (designated as SLEEP2 MODE and is invoked by clearing the IOCE register “SLPC” bit). In the SLEEP2 MODE, the controller can be awakened by-

3NOTE: Vdd = 5V, set up time period = 16.2ms ± 30% Vdd = 3V, set up time period = 19.6ms ± 30%

Product Specification (V1.1) 03.30.2005 • 17

(This specification is subject to change without further notice)