Hacking the DECmate serial port - test-drb@ccmp.vtda.org

29 Apr 2005

...

Subject: Re: Hacking the DECmate serial port
   From: Wai-Sun Chia <waisun.chia at gmail.com>
   Date: Fri, 29 Apr 2005 11:38:17 +0800
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

On 4/29/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
  Not necesarily. The 6402 takes external transmit
and receive clocks, at
 16 times the desirted baud rate. If the clock generator hardware can't go
 faster than 16*4800 for some reason, then you won't get more than 4800
 baud. This is probalby very easy to modify, though. 
Sorry to sound simplistic, but does that mean if I just whack in an
appropriate crystal, then I'd magically get 9600? (haven't downloaded
the prints yet)

Recommendations for an appropriate crystal would be very much appreciated! :-)
How much do you think I could up it to? 19k2?   
The crystal would be 4x whats used for4800!  There are a few yabuts.
One the crystal me DIP osc, two the end freq may exceed the divider 
logics count speed and three the same rock may also supply other 
logic that may not like being sped up like the cpu itself.

Look at the prints first befor you speculate.  The UART itself can 
easily go faster but it's never that easy.

Allison