AT90S/LS4434 and AT90S/LS8535
4
The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running.
Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output buffers can sink 20 mA. As inputs,
Port C pins that are externally pulled low will source current if the pull-up resistors are activated. Two Port C pins can alter-
natively be used as oscillator for Timer/Counter2.
The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running.
Port D (PD7..PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port D output buffers can sink 20 mA. As inputs,
Port D pins that are externally pulled low will source current if the pull-up resistors are activated.
Port D also serves the functions of various special features of the AT90S4434/8535 as listed on page 79.
The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running.
RESET
Reset input. An external reset is generated by a low level on the RESET pin. Reset pulses longer than 50 ns will generate
a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
AVCC
This is the supply voltage pin for Port A and the A/D Converter. If the ADC is not used, this pin must be connected to VCC.
If the ADC is used, this pin must be connected to VCC via a low-pass filter. See page 61 for details on operation of the
ADC.
AREF
This is the analog reference input for the A/D Converter. For ADC operations, a voltage in the range 2V to AV
CC
must be
applied to this pin.
AGND
Analog ground. If the board has a separate analog ground plane, this pin should be connected to this ground plane. Other-
wise, connect to GND.