W79E648 Datasheet, PDF (4/80 Pages) Winbond – Fast 8051 Compatible microcontroller with a redesigned Processor

Preliminary W79E648
3. PIN DESCRIPTION
SYMBOL
EA
TYPE
DESCRIPTIONS
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
I _{address and data will not be present on the bus if EA pin is high and the}
program counter is within 128 KB area. Otherwise they will be present on the
bus.
PSEN
PROGRAM STORE ENABLE: PSEN enables the external ROM data onto the
O Port 0 address/data bus during fetch and MOVC operations. When internal
ROM access is performed, no PSEN strobe signal outputs from this pin.
ALE
O
ADDRESS LATCH ENABLE: ALE is used to enable the address latch that
separates the address from the data on Port 0.
RST
I
RESET: A high on this pin for two machine cycles while the oscillator is running
resets the device.
XTAL1
I
CRYSTAL1: This is the crystal oscillator input. This pin may be driven by an
external clock.
XTAL2
O CRYSTAL2: This is the crystal oscillator output. It is the inversion of XTAL1.
VSS
I GROUND: Ground potential
VDD
I POWER SUPPLY: Supply voltage for operation.
P0.0 − P0.7
I/O
PORT 0: Port 0 is an open-drain bi-directional I/O port. This port also provides a
multiplexed low order address/data bus during accesses to external memory.
PORT 1: Port 1 is a bi-directional I/O port with internal pull-ups. The bits have
alternate functions which are described below:
P1.0 − P1.7 I/O _{T2(P1.0): Timer/Counter 2 external count input}
T2EX(P1.1): Timer/Counter 2 Reload/Capture/Direction control
P2.0 − P2.7
I/O
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.
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