Hacking the DECmate serial port

[Brent Hilpert]

Datasheets for the Harris version of the UART (HD6402) specify a maximum clock rate of 2 MHz and hence a maximum baud rate of 125 KHz (2000/16).
If the current baud rate generator crystal is greater than 16*4800=76.8KHz then it (may) be possible to simply bypass some dividers on the board rather than finding/installing a new crystal.


Wai-Sun Chia wrote:
> 
> 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?
> 
> /ws