Preliminary W78IE54

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2. PORT4

Another bit-addressable port P4 is also available and only 4 bits (P4<3:0>) can be used. This port

address is located at 0D8H with the same function as that of port P1, except the P4.3 and P4.2 are

alternative function pins. It can be used as general I/O pins or external interrupt input sources ( INT2 ,

INT3 ).

Example:

P4

REG

0D8H

MOV

P4, #0AH

; Output data "A" through P4.0

−P4.3.

MOV

A, P4

; Read P4 status to Accumulator.

SETB

P4.0

; Set bit P4.0

CLR

P4.1

; Clear bit P4.1

3. Reduce EMI Emission

Because of on-chip MTP-ROM, when a program is running in internal ROM space, the ALE will be

unused. The transition of ALE will cause noise, so it can be turned off to reduce the EMI emission if it

is useless. Turning off the ALE signal transition only requires setting the bit 0 of the AUXR SFR,

which is located at 08Eh. When ALE is turned off, it will be reactivated when the program accesses

external ROM/RAM data or jumps to execute an external ROM code. The ALE signal will turn off

again after it has been completely accessed or the program returns to internal ROM code space. The

AO bit in the AUXR register, when set, disables the ALE output. In order to reduce EMI emission from

oscillation circuitry, W78IE54 allows user to diminish the gain of on-chip oscillator amplifiers by using

programmer to clear the B7 bit of security register. Once B7 is set to 0, a half of gain will be

decreased. Care must be taken if user attempts to diminish the gain of oscillator amplifier, reducing a

half of gain may affect the external crystal operating improperly at high frequency above 24MHz. The

value of R and C1,C2 may need some adjustment while running at lower gain.

***AUXR - Auxiliary register (8EH)

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AO

AO: Turn off ALE output.

4. Power-off Flag

***PCON - Power control (87H)

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POF

GF1

GF0

PD

IDL

POF:

Power off flag. Bit is set by hardware when power on reset. It can be cleared by software

to determine chip reset is a warm boot or cold boot.

GF1, GF0: These two bits are general-purpose flag bits for the user.

PD:

Power down mode bit. Set it to enter power down mode.

IDL:

Idle mode bit. Set it to enter idle mode.

be used to determine if a reset is a warm boot or a cold boot if it is subsequently reset by software.