8XL51FA/FB/FC
PIN DESCRIPTIONS
VCC: Supply voltage.
V
SS
: Circuit ground.
Port 0: Port 0 is an 8-bit, open drain, bidirectional I/O
port. As an output port each pin can sink several
inputs. Port 0 pins that have 1’s written to them float,
and in that state can be used as high-impedance
inputs.
Port 0 is also the multiplexed low-order address and
data bus during accesses to external Program and
Data Memory. In this application it uses strong internal pullups when emitting 1’s, and can source and
sink several inputs.
Port 0 also receives the code bytes during OTP
ROM programming, and outputs the code bytes during program verification. External pullup resistors are
required during program verification.
Port 1: Port 1 is an 8-bit bidirectional I/O port with
internal pullups. The Port 1 output buffers can drive
several inputs. Port 1 pins that have 1’s written to
them are pulled high by the internal pullups, and in
that state can be used as inputs. As inputs, Port 1
pins that are externally pulled low will source current
(I
IL
, on the data sheet) because of the internal pull-
ups.
In addition, Port 1 serves the functions of the following special features of the 8XL51FX:
Port Pin Alternate Function
P1.0 T2 (External Count Input to Timer/
Counter 2), Clock Out
P1.1 T2EX (Timer/Counter 2 Capture/
Reload Trigger and Direction Control)
P1.2 ECI (External Count Input to the PCA)
P1.3 CEX0 (External I/O for Compare/
Capture Module 0)
P1.4 CEX1 (External I/O for Compare/
Capture Module 1)
P1.5 CEX2 (External I/O for Compare/
Capture Module 2)
P1.6 CEX3 (External I/O for Compare/
Capture Module 3)
P1.7 CEX4 (External I/O for Compare/
Capture Module 4)
Port 1 receives the low-order address bytes during
OTP ROM programming and verifying.
Port 2: Port 2 is an 8-bit bidirectional I/O port with
internal pullups. The Port 2 output buffers can drive
several inputs. Port 2 pins that have 1’s written to
them are pulled high by the internal pullups, and in
that state can be used as inputs. As inputs, Port 2
pins that are externally pulled low will source current
(I
IL
, on the data sheet) because of the internal pull-
ups.
Port 2 emits the high-order address byte during
fetches from external Program Memory and during
accesses to external Data Memory that use 16-bit
addresses (MOVX
@
DPTR). In this application it
uses strong internal pullups when emitting 1’s. During accesses to external Data Memory that use 8-bit
addresses (MOVX
@
Ri), Port 2 emits the contents of
the P2 Special Function Register.
Some Port 2 pins receive the high-order address bits
during OTP ROM programming and program verification.
Port 3: Port 3 is an 8-bit bidirectional I/O port with
internal pullups. The Port 3 output buffers can drive
several inputs. Port 3 pins that have 1’s written to
them are pulled high by the internal pullups, and in
that state can be used as inputs. As inputs, Port 3
pins that are externally pulled low will source current
(I
IL
, on the data sheet) because of the pullups.
Port 3 also serves the functions of various special
features of the MCS 51 microcontroller family, as
listed below:
Port Pin Alternate Function
P3.0 RXD (serial input port)
P3.1 TXD (serial output port)
P3.2 INT0 (external interrupt 0)
P3.3 INT1
(external interrupt 1)
P3.4 T0 (Timer 0 external input)
P3.5 T1 (Timer 1 external input)
P3.6 WR
(external data memory write strobe)
P3.7 RD
(external data memory read strobe)
RST: Reset input. A high on this pin for two machine
cycles while the oscillator is running resets the device. The port pins will be driven to their reset condition when a minimum V
IH2
voltage is applied whether the oscillator is running or not. An internal pulldown resistor permits a power-on reset with only a
capacitor connected to V
CC
.
4