PC Ports at 31.25 Kbps...

[gstopp at fibermux.com]

     I'll have to investigate the Pentium data rates! I've only hacked into 
     486's and down so far...
     
     I've found that on serial cards (old ones, with 8250 UARTs etc.) you 
     can replace the 1.8432MHz crystal with a 6MHz unit, and now your 
     9.6Kbps setting will yield 31.25Kbps. If you can't find a 6MHz, use a 
     12MHz and set the baud rate to 4800.
     
     Even though the older PC hardware architecture gives you the ability 
     to derive the 16x UART clock using a 16-bit divisor, the divide-by-1 
     starts with a base frequency of 115.2Kbps, with /2 giving 57.6K and /3 
     giving 38.4K. The /4 gives you 28.8K, so 31.25K falls between with a 
     divisor of something like 3.6 (which is of course not attainable).
     
     Also - I have been eyeballing those motherboards, such as Gateway2000 
     and Compaq, that have everything integrated (serial ports, video, disk 
     controller), which would make great one-circuit-board embedded CPUs 
     for projects, but they use custom VLSI chips that emulate the UARTs 
     and if you change the 24M or 48M crystal to something that's a 
     multiple of MIDI rates, then the CPU won't even boot. Rats.
     
     Anyway, for what it's worth, if you have old serial cards laying 
     around you can usually hack them to give MIDI data rates.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: In case I missed anything....
Author:  martin.fay at umist.ac.uk at ccrelayout
Date:    2/19/97 7:33 AM


>      * Modifying PC serial ports to work at MIDI rates
     
I've noticed some Pentium boards seem to have an option to run serial 
ports at MIDI rate...so should we seriously think about kludging 
together a serial port MIDI driver, and a breakout box schematic?