Pin Name
Type
Description
P3.0:7
I/O
Port 3:
Is an 8-bit bi-directional I/O port with internal pull-ups. Port 3 pins that have 1’s written to them are pulled
high by the internal pull-up transistors and can be used as inputs in this state. As inputs, Port 3 pins that
are being pulled low externally will be a source of current (IIL, See section ’Electrical Characteristic’)
because of the internal pull-ups.
The output latch corresponding to a secondary function must be programmed to one for that function to
operate (except for TxD and WR). The secondary functions are assigned to the pins of port 3 as follows:
P3.0/RxD: Receiver data input (asynchronous) or data input/output (synchronous) of the serial interface
P3.1/TxD: Transmitter data output (asynchronous) or clock output (synchronous) of the serial interface
P3.2/INT0: External interrupt 0 input/timer 0 gate control input
P3.3/INT1: External interrupt 1 input/timer 1 gate control input
P3.4/T0: Timer 0 counter input
P3.5/T1: Timer 1 counter input
P3.6: Regular I/O port pin
P3.7: Regular I/O port pin
P4.0:1
I/O
Port 4:
Is an 2-bit bi-directional I/O port with internal pull-ups. Port 4 pins that have 1’s written to them are pulled
high by the internal pull-ups and can be used as inputs in this state. As inputs, Port 4 pins that are being
pulled low externally will be a source of current (IIL, on the datasheet) because of the internal pull-up
transistor.
P4.0:
P4.1:
It can drive CMOS inputs without external pull-ups.
RESET
XTAL1
I/O
I
Reset:
A high level on this pin during two machine cycles while the oscillator is running resets the device. An
internal pull-down resistor to VSS permits power-on reset using only an external capacitor to VCC.
XTAL1:
Input of the inverting oscillator amplifier and input of the internal clock generator circuits. To drive the
device from an external clock source, XTAL1 should be driven, while XTAL2 is left unconnected. To
operate above a frequency of 16 MHz, a duty cycle of 50% should be maintained.
XTAL2
O
XTAL2:
Output from the inverting oscillator amplifier.
6
AT89C5115
4128F–8051–05/06
ATMEL [ ATMEL ]
