An Econet Bridge simply joins two Econet network together, this is Acorn's example. The reason for wanting to join two networks together is usually to allow the two networks to run at different clock speeds so that faster computers are not held back by slower ones.
This Bridge doesn't seem to come with any specific documentation but then it doesn't need much to get it working ! It's use is discussed in the Econet Installation Guide. All thats needed is to set the links to assign the two network addresses and thats it.
The Acorn Bridge comes in one of the cheese wedge cases used for co-processors, a word of warning though when working with the lid off e.g. changing the links, watch out for the live mains on the back of the PCB !
The PCB has a small push switch which apparently puts the bridge into a test mode, this isn't documented anywhere. If you put both sides of the bridge on a single network i.e. looped together and monitor Econet traffic then you can see some messages being sent but I'm not sure what they are for ? There is an LED on the board which is usually ON, this flashes when in 'test mode'.
I have made a replica of the Bridge PCB, details can be found here :Replica Acorn Econet Bridge, I have also made a Eurocard version which can be found here: Eurocard Econet Bridge
Here is a dump of the ROM:
Acorn Econet Bridge ROM 2201,281-01.bin