user11802: I am using an ATTINY88 for a project that requires to turn on an LED. Right now I am using pin PA1(ADC7/PCINT25). I noted, however, that when the pin is ON, I get about half the voltage that is connected to Vcc. I checked the voltage in other pins and they are close to Vcc. Will anyone know, what could be the reason for this?
I figure this pin has an internal resistor enable, but I am not certain. 

user7508: You should connect the AVCC pin to VCC. From the datasheet (emphasis
mine):

AVCC is the supply voltage pin for the A/D converter and
  a selection of I/O pins. This pin should be externally connected to
  VCC even if the ADC is not used. [...]
The following pins receive their supply voltage from AVCC:
  PC7, PC[5:0] and (in 32-lead pack- ages) PA[1:0]. All other I/O
  pins take their supply voltage from VCC.


11802: <p>I am using an ATTINY88 for a project that requires to turn on an LED. Right now I am using pin PA1(ADC7/PCINT25). I noted, however, that when the pin is ON, I get about half the voltage that is connected to Vcc. I checked the voltage in other pins and they are close to Vcc. Will anyone know, what could be the reason for this?</p>

<p>I figure this pin has an internal resistor enable, but I am not certain. </p>
 7508: <p>You should connect the AVCC pin to VCC. From the datasheet (emphasis
mine):</p>

<blockquote>
  <p>AV<sub>CC</sub> is the supply voltage pin for the A/D converter <strong>and
  a selection of I/O pins</strong>. This pin should be externally connected to
  V<sub>CC</sub> <strong>even if the ADC is not used</strong>. [...]</p>
  
  <p>The following pins receive their supply voltage from AV<sub>CC</sub>:
  PC7, PC[5:0] and (in 32-lead pack- ages) <strong>PA[1:0]</strong>. All other I/O
  pins take their supply voltage from V<sub>CC</sub>.</p>
</blockquote>
