ATmega88 Pin Functions

Power Ground

Port B is an 8-bit bidirectional I/O port with programmable internal pull-up resistors. Its output buffer has symmetrical driving characteristics and can output and absorb large currents. When used as an input, if the internal pull-up resistor is enabled, the port will output current when it is pulled low by an external circuit. During reset, even if the system clock has not started to oscillate, Port B remains in a high-impedance state. By setting the system clock selection bit, PB6 can be used as the input of the reverse oscillation amplifier and the internal clock operation circuit. By setting the system clock selection bit, PB7 can be used as the output of the reverse oscillation amplifier. When the system uses the internal RC oscillator, PB7..6 can be used as the input port TOSC2..1 of asynchronous timer/counter 2 by setting the AS2 bit of the ASSR register. Port B can also be used for other special functions. Please refer to P66 "Second Function of Port B" and P23 "System Clock and Its Options".

Port C is a 7-bit bidirectional I/O port with programmable internal pull-up resistors. Its output buffer has symmetrical drive characteristics and can output and absorb large currents. When used as an input, if the internal pull-up resistor is enabled, the port
will output current when it is pulled low by an external circuit. During reset, even if the system clock has not started oscillating, Port C remains in a high-impedance state.

When the RSTDISBL bit is programmed, PC6 can be used as an I/O port. Therefore, the electrical characteristics of the PC6 pin are different from those of other port C pins. When the RSTDISBL bit is not programmed, PC6 will be used as the reset input pin Reset. At this time, even if the system clock is not running, a low level that lasts longer than the minimum pulse width on this pin will generate a reset signal. The minimum pulse width is given in P37Table20. A low level that lasts less than the minimum pulse width will not generate a reset signal. Port C can also be used for other special functions, please refer to P69 "Second Function of Port C".

Port D is an 8-bit bidirectional I/O port with programmable internal pull-up resistors. Its output buffer has symmetrical drive characteristics and can output and absorb large currents. When used as an input, if the internal pull-up resistor is enabled, the port will output current when it is pulled low by an external circuit. During reset, even if the system clock has not yet started, Port D is tri-stated. Port D can also be used for other special functions, see P72 "Second Function of Port D".

AVCC is the power supply for the A/D converter. When pins PC3..0 and PC7..6 are used for ADC, AVCC should be connected to VCC through a low-pass filter. When the ADC is not used, the pin should be directly connected to VCC. The power supply for PC6..4 is provided by VCC.

AREF is the analog reference input pin of the ADC.

The ADC7..6 pins of the TQFP and MLF packaged chips are the input ports of two 10-bit A/D converters, and their voltage is provided by AVCC.