ATtiny85 softwareSerial weird characters

Question

I'm trying to send some characters from an ATtiny85 to my PC terminal via an FTDI module.

As ATtiny85 doesn't have hardware UART pins I'm using SW serial connection.

I'm using the 8MHz inner chrystal.

Tested on 300, 600, 1200, 2400, 4800, 9600 bauds without any success, my PC always get 70% wrong chars.

Baud settings were the same on both sides.

My code is:

  #include <SoftwareSerial.h>
  SoftwareSerial sSerial(0, 4); // RX, TX (I DONT USE RX, ONLY TX)

void setup() {
  sSerial.begin(4800);
  delay(1000);
}

void loop() {
  delay(2000);
  sSerial.println("a");
}

It prints extra chars between 'a's.

I've also tried external softserial libs, with no success. I've also tried pullup tx with 1k resistor, with no success. Wires are short, like 5cm/2 inches.

What else should I try? Thanks