Bridges
What it does
Detection
Acorn bridge
SJ bridge
Intro
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Misc h/w
Testing
Misc info
The Acorn bridge
I have very little information on the Acorn bridge. If you can help, if you have an old user guide or an unwanted bridge? Contact me!
Design
The Acorn bridge, in common with the Teletext Adaptor and several other things such as the ARM co-processor system, is housed in the box that is often referred to as "the cheese wedge", which is the same basic profile, material, and colour as the BBC microcomputer, only about half the width. The lame drawing on the right explains the nickname.
There are two network sockets on the back of the box. The one on the left (as you look at the back) is network 'A', while the one on the right is, obviously enough, network 'B.
On the bottom of the box is a Test button. You should never press this while the bridge is connected to a real network as it will cause the network to jam due to junk data from the bridge.
The test is supposed to operate with some sort of loop-back cable.
Setting the network address
There is no NVRAM or clever user interface. To set the network addresses, you must open up the box.
Inside, on the left of the main board, will be a long row of links as two lots of eight links.
The upper eight links set the network address for the network connected to socket 'B', while the lower eight links set the network address for the network connected to socket 'A'.
It works like this, the link being made is a zero bit. If the link is not made, it is a one bit. So you will have to work out how to represent the address in binary, then think it all backwards.
Of each block of eight, the link closest to the rear of the bridge is bit zero. Conversely, the link closest to the front is bit seven.
As far as I was aware, valid networks are in the range 1 to 127, so I would just leave that eighth link well enough alone.
Here is a diagram to aid you:
- Network 'B' is 33 (32 + 1), so all machines on network 'B' will be addressed as
33.xxx. - Network 'A' is 67 (64 + 2 + 1), so all machines on network 'A' will be addressed as
67.xxx.