Date   : Tue, 12 May 2009 09:06:57 +0100
From   : robert@... (Rob)
Subject: BBC B+ Econet weirdness

On 11/05/2009, Michael Firth <mfirth@...> wrote:
>
> Also, does anyone know how the 'collision detectless' operation works -
> the B+ hardware doesn't have the second LM319 fitted, but as far as I
> know is designed to work with the standard NFS 3.60, which was written
> before the B+ was designed?
>
> Finally, does anyone know if there's anything special that would need to
> be done to upgrade the machine to support hardware collision detect,
> beyond adding the second LM319 and passive components listed as 'NF' on
> the B+ schematic?

According to the notes I wrote when I was sweating over the circuits
back in 2004 writing the ADLC emulation for BeebEm:
"~CTS is a NAND of DCD(clock present)(high if valid) &  collission detection!
On the B+ there is (by default) no collission detection circuitary. instead S29
links RTS in it's place, thus CTS is a NAND of not RTS & not DCD"

I'd suggest therefore that adding the missing collision detection
circuitary, and breaking link S29, should be all you need.  The
software side is the same.. (The BeebEm emulation actually emulates
the B+ method, whatever the model of machine, and NFS3.60 seems to
cope.)

Rob.