80-Bus News

Handling the printer was the next problem, characters are output at 9600 baud, which is a lot faster than the printer can print them. The printer has a 1K buffer, but this is soon filled. Fortunately the printer is equipped with a handshake signal which may be connected to pin 2 of SK2, signalling when the buffer is full, or the printer is out of paper, etc. A simple piece of software supervises the printer. Before sending a character the following code is called:

        PUSH AF 3         ; Save the flags and the A register
BUSY    IN A,(0)          ; Get the input into the A register
        RLA 3             ; Move the bit to be tested into the C flag
        JR C, BUSY 3      ; Test and loop if busy
        POP AF

After which the software may direct the character to be sent to the printer.

This finishes my summary of the major changes I have made to my Nascom 1, I hope the above will be of help to someone, and that it will solve some of their problems.

Modifications To Allow The Use Of 2K RAMS
And EPROMS On The Nascom 2.     Jeff Rollason 82