x86/DOS system backup via rs232?

tony duell ard at p850ug1.demon.co.uk
Sun Nov 15 08:28:26 CST 2015

> All Centronics ports have 8 bits going one way, and 4 "handshake" bits
> going the other way.

That's a very PC-centric statement for you, and I am not convinced it's even true 
on IBM PCs and compatibles!

There are plenty of machines that have 7 or 8 data bits output, automatic strobe 
when the CPU writes to that output port and just a single busy pin input.

On the PC, there are indeed 8 data output lines. But there are also 4 more
control output lines that are fully under program control (strobe, etc) and
4 (or is it 5) input lines normally used for printer status input.


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