Date   : Wed, 29 Aug 2007 23:12:07 +0100
From   : pete@... (Pete Turnbull)
Subject: Econet oddities

On 29/08/2007 15:54, Jules Richardson wrote:
> Fragula wrote:
>> Anyone got a schematic for the SJ terminator to post? Thats quite
>> elegant compared with the Acorn one.
> 
> Is it? It seems [1] to be the same as the optional termination within the 
> Acorn socket box (0239,000), but with slightly different values of resistors. 
> I'm surprised Acorn didn't use their same socket box design within their 
> terminators...

The original Acorn terminators, in the same two-tone Vero box as the 
original clock, were active terminators using the same component values 
for which provision was made on early issue Beeb boards.  The later ones 
were passive and consisted of a simple resistor network.

> Or did you mean clock box? That does seem to be a little more involved from 
> how I remember the Acorn one (the only Acorn copy I have is an original 
> "blueprint" on A0 paper and is buried in the loft - I'm not motivated to go 
> and find it :-)

The original Acorn clock in two-tone Vero case was a simple square wave 
generator and divider with provision for different divisions thus 
providing different clock speeds.  The SJ one, from which the later 
Acorn black one is derived, also has provision to vary the mark-to-space 
ratio of the clock, which allows for faster speeds.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York