Date   : Mon, 06 Aug 2007 22:47:21 +0100
From   : julesrichardsonuk@... (Jules Richardson)
Subject: Emulating Econet hardware?

Johan Heuseveldt wrote:
>> One of the more useful issues raised I think was the lack of Econet
>> driver  chips (68B45 from memory??) - I'm not sure what collective
> 
> Almost. It's a 6854 in 2Mhz > 68B54
> 
> 6845 is the CRTC. Not sure if there was a B (=2MHz) version.

Of course it is. Slip of the brain there :-)

>> thoughts were on  finding sufficient numbers[1], emulating one with
>> other off-the-shelf bits, or  using some sort of programmed device for
>> the emulation. I don't think the  Econet chip was a particularly complex
>> device;
> 
> I think it is.

You're right - I found the datasheet for the chip sitting on my fileserver and 
yes, it's significantly more complicated than I remember :-(

>> it was just more convenient to  do it in one larger chip than a
>> handful of common TTL/line drivers/whatever.
> 
> Probably needing a PCB as big as the Beeb itself?
> Just guessing.

I don't think it'd be that bad - but certainly more trouble than it's worth, I 
think.

>  * Several configurations for special control fields at the start
>      of a frame/packet, which can be set to one or two bytes.
>    Econet only uses a single 8 bits 'Address' field (station number)

Hmm - didn't TorchNET make use of non-standard control fields? I'm sure there 
was something which made it incompatible with Econet at a pretty low level, 
even though the hardware was the same (not that we're trying to build a 
TorchNET interface - but it'd be nice if the possibility was still there, I 
suppose)

Didn't something change between early Econet (System and Atom era) versus 
later on (BBC onwards) - or was that only in the driving software rather than 
the really low-level stuff (certainly wasn't the hardware as the older 
interfaces still use the same chip)?

> I could use a few; will contact you by private email.

OK :)

cheers

J.