RE: TED based motherboard

From: Bil Herd (
Date: 2007-04-27 23:14:24

Are you referring to the 14 pin socket next to the LS139?  If so, I am
going to bet that this was an 74LS02 or something similar.  Probably
"decoder helper" for the LS139 next to it in the form of programmable
invertors (I.E. I invert based on a static need or clock or Address
lines).  The first TED had very little external decode, no 82S100 type
logic that I remember, (which was a 24 or 28 pint chip). We needed to
add decode when we needed to latch the keyboard and the banking stuff
for function software as we called it.

If you were to check you should find that an LS02 should match the
connections for inputs and outputs against the way it is wired to the
LS139 and to the pull-up resistors next to it.  

In the "might be a coincidence, might not" department, the C1116
schematic (Thanks shows the refdes to be U103 and U104
which just might match U3 and U4. 

Basically the early TED has less devices to talk to so the address map
is the same, just less specific about who it's talking to.

I say try a TED ROM, it should do something but it wont read keyboard
correctly I would bet.


Bil Herd

-----Original Message-----
From: []
On Behalf Of Anders Carlsson
Sent: Friday, April 27, 2007 8:25 AM
Subject: Re: TED based motherboard

Hello again,

MagerValp wrote on April 4th:

> I played around a bit with flipping bit 3:

Now I have received some spare EPROMs and have time in the weekend to
play around. Did anyone repair the whole 16K of BASIC ROM, or should
I rather burn myself a production ROM for testing? I'll post again if
I make some progress.

The missing chip in U4 worries me, if it might be a 82S100 type PLA.
Based on the ROM dumps, could it be assumed the board has a memory
map at least similar to the finshed 264 prototype? Not that I would
know how to go on from there anyway... :-)

Anders Carlsson

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