From: Marko Mäkelä (msmakela_at_gmail.com)
Date: 2008-03-06 10:03:35
On Thu, Mar 06, 2008 at 09:41:10AM +0100, Anders Carlsson wrote:
> The more I think about it, the less feasible the tape port is for this
> purpose. Even if we transmit a boot loader with a menu software upon
> pressing SHIFT+RUN/STOP, how will the PC server or USB device know which
> option the user selects from the keyboard if the only signal that is sent
> out is CASS READ? The server would again have to transmit every
> application on the hard disk in round-robin order until the computer
> recognizes the program it wants to load. Urgh. Even at 38400 bps, it may
> take a while.
Actually, the C2N232 does implement a bidirectional protocol that
cbmlink uses. cbmlink would not work without a bidirectional protocol.
c2nload uses the protocol for fast-loading the payload at 38400 bps.
You can see the timing diagrams of the C2N232 protocol here:
http://www.iki.fi/~msmakela/8bit/c2n232/firmware/timing.png
The Commodore sends 4 bits at a time by a varying pulse width,
and the C2N232 sends 1 bit at a time.
I could have used the SENSE and MOTOR lines as well, but the MOTOR line
would probably have some delay, and SENSE was hooked up in a weird way
in some Commodore model (perhaps the 264 series: C16, C116, plus/4).
Marko
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