w78l812a Winbond Electronics Corp America, w78l812a Datasheet - Page 6

• Manufacturer Part Number: w78l812a
• Description: 8-bit Mcu Series 80c51-based
• Manufacturer: Winbond Electronics Corp America

4. PIN DESCRIPTION
P0.0
P1.0
P2.0
P3.0
P4.0
SYMBOL
XTAL1
XTAL2
PSEN
RST
ALE
V
V
EA
DD
SS
−
−
−
−
−
P0.7
P1.7
P2.7
P3.7
P4.6
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 data will not be
present on the bus if EA pin is high and the program counter is within on-chip ROM area.
Otherwise they will be present on the bus.
PROGRAM STORE ENABLE: PSEN enables the external ROM data onto the Port 0
address/data bus during fetch and MOVC operations. When internal ROM access is
performed, no PSEN strobe signal outputs from this pin. This pin also serves the alternative
function P4.6.
ADDRESS LATCH ENABLE: ALE is used to enable the address latch that separates the
address from the data on Port 0.
RESET: A high on this pin for two machine cycles while the oscillator is running resets the
device.
CRYSTAL1: This is the crystal oscillator input. This pin may be driven by an external clock.
CRYSTAL2: This is the crystal oscillator output. It is the inversion of XTAL1.
GROUND: Ground potential
POWER SUPPLY: Supply voltage for operation.
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.
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
INT2
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.
PORT 3: Port 3 is a bi-directional I/O port with internal pull-ups. The pins P3.4 to P3.7 can
be configured with high sink current which can drive LED displays directly. All bits have
alternate functions, which are described below:
RXD(P3.0): Serial Port receiver input
TXD(P3.1): Serial Port transmitter output
T0(P3.4): Timer 0 External Input
T1(P3.5): Timer 1 External Input
PORT 4: A 5-bit bi-directional I/O port which is bit-addressable. Pins P4.0 to P4.3 are
available on 44-pin PLCC/QFP package. P4.6 is the alternative function corresponding to
INT0 (P3.2): External Interrupt 0
INT1 (P3.3): External Interrupt 1
RD (P3.7): External Data Memory Read Strobe
PSEN .
WR (P3.6): External Data Memory Write Strobe
−
INT9 (P1.0
−
P1.7): External interrupt 2 to 9
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DESCRIPTIONS
W78LE812/W78L812A