Newsgroups: comp.sys.transputer
From: paul@walker.demon.co.uk (Paul Walker)
Subject: Re: Building A TRAM
Organization: Paul Walker Consultancy
Date: Fri, 26 Aug 1994 07:14:45 +0000
Message-ID: <777885285snz@walker.demon.co.uk>

In article <33hsl1$lqb@wimbledon.dcs.hull.ac.uk>
           d.r.smith@e-eng.uk.ac.hull "Dave Smith" writes:

>HELP!
>
>Two of us here have been trying to build a transputer based 
>robot controller and we are having no luck whatsoever. We have
[...]
>What we have is a T225, with link 1 wired as in the Transputer Technical
>Notes, BootFromROM low, and the rest of the pins as they should be according
>to the data (as far as we know).
>When we run a worm, either the B008 one or the TDS2 one, the T225 receives 
>a packet on Link1In and sends an acknowledge, but that's it, finished. The
>worm doesn't recognise it and nowt else happens.

Familiar experience to most hardware engineers! Actually the transputer has 
far fewer pins that need to be held in some state than any other 
processor, but the list extends longer than the ones you mentioned.

The fact you get an acknowledgement means the clock is ok, and probably
that Reset is ok. Other possibilities are:

Analyse: Hold low
MemWait: Hold low if you are using fast enough RAM or on-chip only
MemReq: Hold low particularly during booting, and permanently if you are 
        not using some form of DMA/shared memory
All other Link inputs: Hold low through a 10k resistor. If a link floats, 
        the transputer decides to boot from that link and can't tell that
        it is booting rubbish.

Most likely culprit is MemReq or another link.

Be aware that when you look at a floating input with a 'scope, the probe
pulls the input low --- so sometimes things start to work when you put
the probe on! A logic probe tells you whether the pin is high, low, 
or floating.

If you check these, they are all held low, and you still have a problem,
let me know. And I suppose I'd like to hear that you have got your set-up
to work --- which I hope you can do today.

Paul Walker              Consultancy in product specification and design
+44 (0)1275 844864       (and Trams and transputer links sometimes)
paul@walker.demon.co.uk


