#include <SoftwareSerial.h>

                // *** Define the RX and TX pins.a
                
                #define TX   4  // PB3, Pin 2 on attiny45 leg
                #define RX   3  // PB4, Pin 3 on attiny45 leg
                
                SoftwareSerial mySerial(RX, TX);
                
                char chr;
                
                void setup() {
                  // initialize serial communications at 9600 bps:
                
                  mySerial.begin(9600);
                  pinMode(TX,INPUT);
                  pinMode(0, OUTPUT);
                }
                
                void loop()
                
                {
                  char chr = mySerial.read();
                  mySerial.read();
                
                  if (chr == 'a') {   
                     digitalWrite(0, HIGH);
                      pinMode(TX,OUTPUT);
                      mySerial.print(chr);
                      delay(1000);
                      pinMode(TX,INPUT);
                      digitalWrite(0, LOW);
                  }

                  else
                  {
                     digitalWrite(0, LOW);
                  }
                
                }