Arduino example demonstrates how to print ASCII values in decimal, hexadecimal, octal, and binary.

ArduinoAsciiConverter

#include <Arduino.h>

int character = 0;

void setup()
{
  Serial.begin(9600);
  Serial.print("Echo start\r\n");
}

void loop()
{
  if (Serial.available() > 0)
  {
    character = Serial.read();

    Serial.print("ascii: ");
    Serial.write(character);
    Serial.print("\t\tdec: ");
    Serial.print(character);
    Serial.print("\t\thex: ");
    Serial.print(character, HEX);
    Serial.print("\t\toct: ");
    Serial.print(character, OCT);
    Serial.print("\t\tbin: ");
    Serial.println(character, BIN);
  }
}

Linux:
stty -F /dev/ttyUSB0 cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts

tail -f /dev/ttyUSB0
ascii: A		dec: 65		hex: 41		oct: 101		bin: 1000001
ascii: a		dec: 97		hex: 61		oct: 141		bin: 1100001

echo -n "Aa" > /dev/ttyUSB0