Date : Fri, 14 Aug 2009 20:46:36 +0100
From : bbcmicro@... (Ian Stocks)
Subject: econet bridge protocol
Johan Heuseveldt wrote:
> Both damaged line drivers are AM26LS30; '30' for short. Replacing
> both with a new one, didn't work as aspected though. In the end I
> needed a '30' for IC14, and a '34' for IC16, just as in the other
> bridge. Both bridges are the same with a PCB of '0237,000 Iss.2'.
> There are no modifications found on both of them, including back side.
http://acorn.chriswhy.co.uk/Network/Pics/Acorn_AEH20_EconetBridge_HR.html
That picture matches my bridge, so IC 14 should be AM26LS30 (dual
driver), IC 16 should be AM26LS34 (quad receiver).
> Within 5 seconds after powering up, IC16 is too hot to touch. At
> first I didn't notice, and for 20 minutes or so, the bridge was on.
> When used in the 'good' bridge, the chip was still functioning!
> OK, the data sheet say they have Short Circuit Current Limit, but it
> can not last for ever!
>
> Please note that the actual line drivers are in IC 14, closest to
> the Crystal. This IC 14 is used as
>
> Dual Differential Line Drivers (EIA-422-A)
>
> and each one is driving the net data on their nets A and B.
>
> The other one, IC 16 and closest to one of the 68B54, is used as
>
> Quad Single Ended Line Drivers (EIA-423-A)
Not sure where you got the description from but they should be quad
recievers, 2 for each network, 1 on each network for the clock signal,
and 1 for data signal on each net. The bridge uses a reciever chip, all
other econet hardware uses LM319 Comparators for the data and clock
signals. http://www.national.com/mpf/LM/LM319.html
>
> and this makes several connections between the two networks, as
> reported a while back. :-)
I can only assume your looking at the wrong datasheet pinout to come to
that conclusion. Try http://www.datasheet4u.com/download.php?id=493144
> Perhaps some diagnostic or test hard ware?
Nope.
> It seems to me that these '30' ones are not the same as they used
> to be, and IC 16 can no longer be such one. Instead, it must be a '34'.
> The Dutch person, who responded earlier, also confirmed this similar
> situation.
IC14 and IC16 are very different, and not interchangable.
Ian.