B3-13

EM78P156E

• The Watchdog Timer and prescaler are cleared.

• Upon power-on, the upper 3 bits of R3 are cleared.

• The bits of the CONT register are set to all “1” except 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 register and bits 0~2 of IOCF register are cleared.

Executing the “SLEP” instruction can perform the sleep mode (power-down mode). While entering sleep

mode, WDT (if enabled) is cleared but keeps 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 changed (if enabled).

The first two cases will cause the EM78P156E 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 vector following

wake-up. If ENI is executed before SLEP, the instruction will begin to execute from the address 008H after wake-

up. If DISI is executed before SLEP, the instruction will restart from the place where is right next to SLEP after

wake-up.

Only one of the cases 2 and 3 can be enabled before entering the sleep mode. That is,

[a] if Port 6 input status changed interrupt is enabled before SLEP , WDT must be disabled by software; however,

the WDT bit in the option register is still enabled. Hence, the EM78P156E can be awakened only by case 1 or 3.

[b] if WDT is enabled before SLEP, Port 6 input status changed interrupt must be disabled. Hence, the EM78P156E

can be awakened only by case 1 or 2. Refer to the section on interrupt.

If Port 6 input status changed interrupt is used to wake up the EM78P156E (the case [a]), the following

instructions must be executed before SLEP:

MOV A, 0bxx000110

; Select internal TCC clock

CONTW

CLR R1

; Clear TCC and prescaler

MOV A, 0bxxxx1110

; Select WDT prescaler

CONTW

WDTC

; Clear WDT and prescaler

MOV A, 0b0xxxxxxx

; Disable WDT

IOW RE

MOV R6, R6

; Read Port 6

MOV A, 0b00000x1x

; Enable Port 6 input changed interrupt

IOW RF

ENI (or DISI)

; Enable (or disable) global interrupt

SLEP

; Sleep

NOP

One problem should be aware that after waking up from the sleep mode, WDT would enable automatically.

The WDT operation (being enabled or disabled) should be handled appropriately by software after waking up from

the sleep mode.