Char Send - sends characters to the 1401 and checks that they are successfully transferred from the PC to the 1401 interface card.

Char Read - sends very simple commands to the 1401 and checks that the 1401 responds correctly.

Good Data - sends commands to the 1401 and checks that the replies are correct.

Bad Data - sends invalid commands and checks that the 1401 detects errors and reports them.