ELANsat Tech OTP ROM EM78P156N User Manual

Page 20

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EM78P156N

OTP ROM

4.5 RESET and Wake-up

1. RESET

A RESET is initiated by one of the following events-

(1) Power on reset.

(2) /RESET pin input "low", or

(3) WDT time-out (if enabled).

The device is kept in a RESET condition for a period of approx. 18ms

1

(one oscillator start-up timer period)

after the reset is detected. Once the RESET occurs, the following functions are performed. Refer to Fig.9.

• The oscillator is running, or will be started.

• The Program Counter (R2) is set to all "0".

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

• The Watchdog timer and prescaler are cleared.

• When power is switched on, the upper 3 bits of R3 are cleared.

• The bits of the CONT register are set to all "1" except for the Bit 6 (INT flag).

• The bits of the IOCA register are set to all "1".

• The bits of the IOCB register are set to all "1".

• The IOCC register is cleared.

• The bits of the IOCD register are set to all "1".

• Bit 7 of the IOCE register is set to "1", and Bits 4 and 6 are cleared.

• Bits 0~2 of RF and bits 0~2 of IOCF register 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), or

(3) Port 6 input status changes (if enabled).

The first two cases will cause the EM78P156N to reset. The T and P flags of R3 can be used to determine the

source of the reset (wake-up). The last case is considered the continuation of program execution and the

global interrupt ("ENI" or "DISI" being executed) decides whether or not the controller branches to the interrupt

1

NOTE: Vdd = 5V, set up time period = 16.8ms ± 30%

Vdd = 3V, set up time period = 18ms ± 30%

This specification is subject to change without prior notice. 20

07.29.2004 (V1.2)

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