Re: Mark IV Electronics Design

[Tom Droege <droege@FNAL.GOV>]

This has been suggested several times.  The ethernet cable does not 
answer the question of buffering.  The camera will generate 32 Mbytes
in one continuous block.  I don't want to interrupt this data flow as
that is the kind of thing that causes pattern errors in the data.  So
the data is transmitted by a cable of my own design to a memory card
that lives in a PC.  

Now you can have an ethernet cable on that PC to move the data to where
you want to work on it.  Just consider the first PC in the string to 
be part of the Mark IV control system if you like.  A control program 
can live there and could now communicate by ethernet.  

Even if someone tells me that ethernet can accept data at a continuous
1Mbyte rate for blocks 32 Mbytes long, still the easiest way for me to
build an ethernet interface would be to put a memory card in a PC and
have the PC drive the ethernet cable.  PCs are cheap.  I could buy an
extra PC for all the Mark IVs apt to be built for less than the cost
of designing even a simple interface to ethernet.  

I certainly did consider derandomizing bufferes of various types.  Since
memory is so cheap, it was simply easier to build a big buffer.  We 
avoided the complication of designing it for simultaneous reads and writes.
Just data push it full, and have the PC unload it before the next data
push.  Multiple buffers can now be done in the PC.

As I say, consider the first PC just the buffering and Ethernet interface.

Tom Droege

At 03:37 PM 1/27/98 -0200, you wrote:
>On Thu, 8 Jan 1998, Chris Albertson wrote:
>
>> Tom Droege wrote:
>> > 
>> > This is mostly a reply to Grzegorz Pojmanski who is interested in using the
>> > Mark IV electronics.  I am posting it to the group as there may be general
>> > interest.   The status today is that there are rough drawings for
everything.
>> > The connector details have not been worked out. 
>> 
>> If you have not yet worked out the cable that feeds the
>> memory board would you make it look like a printer
>> interface.  Modern printer ports are bi-directional
>> and very fast. (Just look at what a ZIP drive can do.) 
>[...]
>
>Depending on neeeds, it may beinteresting to see an ethernet like cable to
>connect. Why this? 
>
>If we have need to transfert a lot of data in very restric time interval,
>eg CCD camera, the ethernet link is fast enough. The paralel port cables
>are limited on distance for very high speed.
>
>As exemple, a CCD camera builder in France may fournish its camera with
>dedicated ethernet link for lower price that a paralel port and the
>estimated time for transfer is great better.
>
>Dietmar William Foryta (foryta@fisica.ufpr.br)
>
>
>