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[aprssig] Re: MFJ 1270B

Stephen H. Smith wa8lmf2 at aol.com
Sun Jan 1 02:42:34 UTC 2006

fred at wb4aej.com wrote:
> Bruce,
>     Yes, I have already installed UIView on my PC, though I haven't yet
> mastered its use (and I say that tongue in cheek).
>     I popped the cover.  I see the firmware in one of three DIP sockets in a
> row.  The middle one is empty.
>     In that case, is the TAPR firmware upgrade worth the cost or should I
> let it ride?
>     I would like to stick a little more memory in there, though.  Maybe I
> can find some on Ebay.  Or maybe you folks know what I need and where to
> find it at a good cost.
>     73,

1)   At some point, MFJ dropped KISS support to make room for other 
features in their firmware -- not certain when they started 
non-supporting it.  Test it in KISS mode and see if it works.   

The original TNC2 design (of which the MFJ is a near clone) used two 8K 
static RAMS and a 27128 EPROM. These three chips filled all three 
sockets.  The board layout provided support for anticipated  future 
higher density stat RAMS.   A movable jumper on the board provided for 
addressing two 8K RAMS or a single (at the time horribly expensive) 32K  

Within a few years the single 32K RAM became standard, the jumper was 
bridged with a PC board trace that had to be slashed with an X-acto 
knife if you  wanted to downgrade to the dual 8K configuration, and the 
second socket has remained empty ever since.  

There is no point in adding memory; indeed you CAN'T add memory.  This 
thing is NOT a PC capable of addressing hundreds of megabytes of RAM.   
The entire memory address space of the Z-80 CPU in the TNC is only 64K!! 
   The 32K RAM occupies half of the memory space; the firmware in the 
27256 (32K  bytes) EPROM already occupies the other half.   The entire 
TNC firmware is hand-coded directly in Z-80 assembly code and takes a 
fraction of the RAM and ROM that typical PC apps take.  

Bear in mind you are not running Microsoft bloatware, written in 
high-level languages with a graphical interface, that occupies 10s or 
100s of MB in the TNC (although you may well be on the PC attached to 
the TNC's serial port). Think of the miniscule amounts  of memory that 
8-bit CP/M and Apple ][ programs required compared to todays stuff!

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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