[aprssig] MFJ Fill-In Digi setup

Stephen H. Smith wa8lmf2 at aol.com
Thu Feb 19 23:18:12 CST 2009

Clay Melhorn wrote:
> Hello Cap,
> Sounds great, most of the time the digi will run stand alone tnc.  I 
> need to know if once the replacement chip is installed will the tnc 
> still work with UIView32 from my PC when I need to monitor the local 
> traffic and mapping?  If that is the case I will send away for the chip.

1)  You don't "send away" for the chip.  You edit the UIdigi overlay 
text file with your personal data (callsign, coordinates, beacon 
messages and intervals, etc), merge this (using a special UIdigi 
utility) with the binary file containing the actual digi program, and 
then program the modified binary file into a 27256 or 27512 eprom 

Or ask for the help of someone, like myself, that has an eprom 
programmer device that will do eproms for others.

One real advantage of UIdigi is that your personalized settings 
(callsign, beacon texts & intervals, lat/long, symbol codes, etc are 
literally "frozen in stone" in the eprom firmware.  Because of this, 
your settings don't get lost with power failures, accidental resets, 
dead backup batteries, etc.

2)  UIdigi does not provide normal TNC operation -- it is solely a 
stand-alone dedicated digipeater.    I have been hoping for years that 
the author might at least incorporate receive-only operation; ie echo 
whatever the digi hears out the serial port.  I brought this up on the 
UIdigi mailing list about 8 years ago.   Unfortunately, further 
development of UIdigi seems to have ceased.  

One approach is to make a "double-decker" eprom.  Either UIdigi or the 
original firmware occupies a 27256 eprom. You can use a 27512 (twice as 
large) and place the OEM firmware in one half and UIdigi in the other.   
When you insert the 24-pin eprom into the socket, bend pin 1 so it 
misses the socket.    Then wire a  single pole double-throw toggle 
switch to this pin so you can either ground pin 1 or connect it to +5 

With the switch in one position, the original fimware is active for use 
with UIview.  Flip the  switch the other way, cycle the power off and 
back on, and the stand-alone UIdigi mode is enabled.  



Stephen H. Smith    wa8lmf (at) aol.com
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