[Coco] Hello Aaron help dragon

[Mark Marlette]

Darren,

Can you briefly explain your Turbo methodology for DW4 using the extra lines? Faster slew rate with higher drive current?

TIA,

Mark
Cloud-9

----- Original Message -----
From: "Darren A" <mechacoco at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Tuesday, May 17, 2011 9:55:39 AM
Subject: Re: [Coco] Hello Aaron help dragon

On 5/16/11, Aaron Wolfe  wrote:
>
> <snip>
>
> The client side stuff is where it might get tricky for Dragon support.
>  As I understand it, rather than a bitbanger, the Dragon has a 6551
> uart.  That's good for most things, but bad for DriveWire.  The 6551
> just can't go as fast as Darren's bitbanger code.  I think 57,600
> might be possible, not entirely sure.  That isn't horrible but it
> would be slower than a real floppy.   The other option would be to use
> the parallel port found on the Dragon.  This could be quite fast, and
> the DW server could support parallel devices with just a few changes.
>  There was a cool project sort of like DriveWire for the dragon that
> used the parallel port, called pc-share.  it isn't under development
> any more but it might provide everything the dragon users need.
>


The Dragon 64 serial port is crippled by the same level-shifting
circuitry used in the CoCo 1, resulting in the 38400 bps limit.
However, the 6551 in the Dragon cannot operate at 38400 bps with the
supplied crystal.  Unless you make hardware modifications, the Dragon
serial port is limited to only 19200 bps.

The 8 data lines of the Dragon's parallel port are wired for output
only, so you can't do bi-directional parallel I/O.  It should be
fairly simple to connect an inexpensive TTL to RS232 level shifter
module to a few of the pins on the parallel port, creating a
high-speed bit banger port adapter.  There are 2 input pins on the
parallel port (ACK and BUSY*) which could be used along with any one
of the outputs to achieve 115200 bps using the new technique in DW4
(turbo).

Darren

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