Date   : Sun, 26 Nov 2006 15:07:24 +0000 (GMT)
From   : chris@... (Chris Johns)
Subject: Econet things...

On Sat, 25 Nov 2006, BRAHMS wrote:

> I'd like to lash up a clock box over the next few days but don't have 
> any line drivers to hand. Does anybody know, could I just do something 
> quick and dirty with opposing 5V/0V signals on the opposing clock+/- 
> lines or is that insufficient? (To start off with I just want to connect 
> a couple of machines...)

I have seen a circuit diagram for a 555 based clock, but I'm pretty sure 
it needed a line driver of some sort. I'd be weary of randomly shoving 
5V/0V on the clock+- lines - you could end up needing a load of line 
drivers to replace ones you've fried. I don't know if it would work or 
not, but I'd need to find out a lot more before i risked it!

> In the longer run I've been thinking of making a USB->Econet adaptor so 
> I can serve files from Linux...with the right software we could all 
> connect up over the internet???

This has been discussed many times on this list. Someone was looking at an 
ethernet - econet gateway, but i'm not sure what became of it. AIUI, the 
problem with using the 6854 on anything USB based is latency. The ADLC has 
something like a 3 byte buffer, so if you can't fill that quickly enough, 
you're going to get problems.

On the beeb it's done with NMIs, but if you're the far side of the USB bus 
you're going to need some local buffer and local processing to fill it. 
The Econet ISA cards had a 6502 on them and some RAM to do this.

If you do your own implementation, you may be able to sidestep some of 
these problems, of course.

> Does anybody know of any alternatives to the ADLC 68B54 that are readily 
> available? If not would it be reasonable to try and emulate one using a 
> microcontroller?

While the 6854 is no longer "available", how many are around? I've 
probably got a fair number somewhere in a box, and others probably have 
too.

> I'm also guessing; all the other line driver circuitry can be any old 
> ISO-422 compliant chips I can source (there seems to be plenty of choice 
> on RS)

Are the line drivers used in the master module still available?

In fact, there must be loads of the master Econet modules around. I think 
can can be 'hacked' into a beeb, but I've never tried it (as both my Bs 
have Econet fitted anyway). They are pretty much the ADLC and everything 
network side of it.

-- 
  Chris Johns <chris@...             >