Preliminary W78LE54

Publication Release Date: February 1999

- 3 -

Revision A1

PIN DESCRIPTION

SYMBOL

DESCRIPTIONS

EA

EXTERNAL ACCESS ENABLE: This pin forces the processor to execute out of

external ROM. It should be kept high to access internal ROM. The ROM address and

within on-chip ROM area.

PSEN

address/ data bus during fetch and MOVC operations. When internal ROM access is

ALE

ADDRESS LATCH ENABLE: ALE is used to enable the address latch that separates

the address from the data on Port 0.

RST

RESET: A high on this pin for two machine cycles while the oscillator is running resets

the device.

XTAL1

CRYSTAL1: This is the crystal oscillator input. This pin may be driven by an external

clock.

XTAL2

CRYSTAL2: This is the crystal oscillator output. It is the inversion of XTAL1.

GROUND: Ground potential

POWER SUPPLY: Supply voltage for operation.

P0.0

−P0.7 PORT 0: Port 0 is a bi-directional I/O port which also provides a multiplexed low order

address/data bus during accesses to external memory. The pins of Port 0 can be

individually configured to open-drain or standard port with internal pull-ups.

P1.0

−P1.7 PORT 1: Port 1 is a bi-directional I/O port with internal pull-ups. The bits have alternate

functions which are described below:

T2(P1.0): Timer/Counter 2 external count input

T2EX(P1.1): Timer/Counter 2 Reload/Capture control

P2.0

−P2.7 PORT 2: Port 2 is a bi-directional I/O port with internal pull-ups. This port also provides

the upper address bits for accesses to external memory.

P3.0

−P3.7 PORT 3: Port 3 is a bi-directional I/O port with internal pull-ups. All bits have alternate

functions, which are described below:

RXD(P3.0) : Serial Port receiver input

TXD(P3.1) : Serial Port transmitter output

INT0 (P3.2) : External Interrupt 0

INT1

(P3.3) : External Interrupt 1

T0(P3.4)

: Timer 0 External Input

T1(P3.5)

: Timer 1 External Input

WR

(P3.6) :External Data Memory Write Strobe

RD

(P3.7) : External Data Memory Read Strobe

P4.0

−P4.3 PORT 4: Another bit-addressable bidirectional I/O port P4. P4.3 and P4.2 are

alternative function pins. It can be used as general I/O port or external interrupt input