[aprssig] MFJ1278 and UI-DIGI

Ron Stordahl ron.stordahl at digikey.com
Sat Mar 12 07:31:28 CST 2005

Andrew Rich wrote:

>TNC MFJ-1278 has a 27C512 PROM
>Do I need to program up a 512 ?
>Or can I change jumper 15 (256/512) 
>Cheers Andy VK4TEC

The following is quoted from the 'files' section of the UIDIGI yahoo 
group.  I believe the MFJ1278 is the same board, but perhaps with 
different factory firmware (which you will replace).  The reason to use 
a 27C512 is if you are running something like TheNet/X1J4 which would 
not fit on a 27C256.  All you will need for UIDIGI is a 27C256 with the 
settings as described below:


Converting a stock MFJ-1270C Rev 11 for UIDIGI use:

1) Remove (if any) existing jumper on JMP-9.
2) Remove the chip at U40.
3) Verify jumper on JMP-15 is 1 to 2.
4) Place jumper on JMP-16
5) Verify there is NO jumper on JMP-21
6) Remove the chip at U23 and replace with UIDIGI firmware. Take
care to see that the 'notch' is to the left, i.e. closest to JMP15.
7) Momentarily short JMP-23 to reset TNC.  This is most easily done
by moving the shorting jumper on JMP-5 to JMP-23 and back to JMP-5.

Guide to location of the jumpers:  JMP-9 is between U16 and U20,
JMP-15 and JMP-16 are next to U23.  JMP-21 is next to U22.  JMP-5
and JMP-23 are next to the battery.

I used a 'one time programable' Amtel AT27C256R as the ultra violet
erasable 27C256's are becomming hard to find and expensive. You
should save the original chips from U40 and U23 in case you wish to
restore the unit to stock condition.

There are two types of 'DIP' switches MFJ has used for baud rate.
The most common is a 'lever' type.  For that type the UP position
corresponds to OPEN.  The switch is labeled and you should confirm
that up is OPEN.  If so set those switches thus:


The other type is a 'slide' type.  On those up is ON and down is OPEN,
just the opposite of the more common type.  The switch is labeled, you
should confirm the markings.  If so set those switches thus:


Connection was made to the unit with a standard modem cable at
9600/8/N/1 using a standard terminal emulator such as HyperTerminal.

Ron, N5IN

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