Date   : Sun, 29 Mar 2009 20:57:19 +0100
From   : mfirth@... (Michael Firth)
Subject: A few Econet questions

----- Original Message ----- 
From: "Phil Blundell" <philb@...>
To: "Michael Firth" <mfirth@...>
Cc: <bbc-micro@...>
Sent: Sunday, March 29, 2009 7:30 PM
Subject: Re: [BBC-Micro] A few Econet questions


> On Sun, 2009-03-29 at 18:24 +0100, Michael Firth wrote:
>> Does anyone here know anything more about the unpopulated IC4 on the
>> newest of the Acorn Econet modules?
>>
>> [...]
>>
>> There is a suggestion that it is for allowing the interface to provide
>> a clock to the Econet, and the connections from the unpopulated IC
>> directly to two pins of the header that connects to the Econet
>> connector seems to also point to this.
>
>>From the photos at the links you mentioned, I would guess that IC14 is
> intended as an alternative to IC7, perhaps as a design backup in case
> the surface-mount part was unobtainable for some reason.  It's hard to
> tell from the photos alone though and I don't have one of those boards
> to look at.
>
> Which pins on the Econet header is this IC actually connected to?  Can
> you see where any of the other tracks go to?
>
>From closer examination, the mystery IC4 chip is actually connected to pins 
1 and 2
of PL2, which are the data pins, not the clock pins.

The 4 PCB links that also initially look mysterious are actually hard wired 
with PCB
tracks on the back, so aren't an optional selection after all.

>From looking at the datasheets, your suggestion of a through-hole 
alternative to IC7
seems very likely, as IC7 is the 26LS30 line driver, and IC4 actually has 
the correct
pinout to be the DIP version of the same IC (e.g. power and ground are in 
the correct
places, and the pins connected to PL2 would be the output pins of the 
driver)

I guess there goes my hope of a cheap way of generating an Econet clock :-(

For reference, I also just found that the BOM for this board is in the A3020 
Technical
Reference Manual, available from 
http://acorn.chriswhy.co.uk/Computers/A3020.html.

Wish I'd done a bit more checking and searching before asking now!

Regards

Michael