W78E54

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Flash

No function in this mode.

MODE

DESCRIPTION

Normal

This pin forces the processor to execute a program from the external ROM. When the

internal flash EEPROM is accessed as in the W78C54, this pin should be kept high.

Flash

This pin accepts the high voltage (12V) needed for programming the flash EEPROM.

RST

MODE

DESCRIPTION

Normal

RST, Reset, Input, active high.

This pin resets the processor. It must be kept high for at least two machine cycles in

order to be recognized by the processor.

Flash

Flash mode configuration pin, Input, active high.

RST is used to configure the flash operations. For details, see

Flash Operations.

ALE

MODE

DESCRIPTION

Normal

ALE, Address Latch Enable, Output, active high.

ALE is used to enable the address latch that separates the address from the data on

Port 0. ALE runs at 1/6th of the oscillator frequency. A single ALE pulse is skipped

during external data memory accesses. ALE goes to a high impedance state with a

weak pull-up during reset state.

Flash

Flash mode configuration pin, Input, active low.

ALE is used to configure the flash operations. For details, see

Flash Operations.

PSEN

MODE

DESCRIPTION

Normal

PSEN, Program Store Enable, Output, active low.

This pin enables the external ROM onto the Port 0 address/data bus during fetch and

MOVC operations. PSEN goes to a high impedance state with a weak pull-up during

reset state

Flash

Flash mode configuration pin, Input, active high.

PSEN is used to configure the flash operations. For details, see

Flash Operations.

XTAL1

MODE

DESCRIPTION