80-Bus News

28

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

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