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[aprssig] Re: MFJ 1270B

Fred Atkinson, WB4AEJ fred at wb4aej.com
Sun Jan 1 03:11:45 UTC 2006

> 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.

    Not sure how to do that.  Haven't found documentation on the current
commands anywhere as yet.  But according to the manual (the 1270C manual, I
couldn't find the one for the 1270B), it does indeed support KISS mode.

> 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
> RAM.
> 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.

    According to the manual, memory can be increased to 512 kilobytes.  I'm
still trying to find the specifics on the type of memory required.

> 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!

    I am aware of that.  I operated from a CUI for years.  I even programmed
in Fortran on punch cards at one time (sixties/seventies timeframe, of
course).  But if I can upgrade for low cost (like finding it on Ebay), why
not?  All that is required is to change a couple of option jumpers.

> EchoLink Node:      14400    [Think bottom of the 2M band]

    I love your node number.  I registered 8773 myself, but I've still not
used it.  I need to upgrade my PC before I'm going to have much luck with
Echolink or video over IP.

> "APRS 101"  Explanation of APRS Path Selection & Digipeating
>   http://webs.lanset.com/wa8lmf/DigiPaths

    This is something I'm going to have to check out.

> Updated APRS Symbol Chart
>   http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf

    This, too.

> New/Updated "Rev G" APRS     http://webs.lanset.com/wa8lmf/aprs
> Symbols Set for UI-View,
> UIpoint and APRSplus:

    Well, I'll look at this, too.


Fred, WB4AEJ

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