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lyonadmiral
August 7th, 2011, 03:35 PM
If you had that many to play with, would it be theoretically possible to connect 3 or 4 expansion units to a 5150?

Chuck(G)
August 7th, 2011, 03:55 PM
I don't know anyone who's tried it, but it might be possible--remember that the expansion unit adds wait states--which is why it's a bad idea to put memory expansion cards in one.

mkemp
August 16th, 2011, 11:00 AM
No reason why not, except for the memory card limitation Chuck(G) mentioned. I don't remember what else won't work in one. What would you put in them, though? About the only thing I can think of are more disk drives with controllers that have jumpers to keep the BIOSen from stepping on one another. Two full-height or four half-height drives in each unit.

per
August 16th, 2011, 11:14 AM
I actually think it would be quite problematic. First of all, there is a reason why that waitstate is added. The cable and cirquits on one set of extender/receiver cards does add quite a lot of delay, which may be problematic for slower memory or I/O devices if no waitstate was added.

The first problem with several cards in series would be that each set of receiver/extender cards of the chain would add delay, but the number of waitstates would never exceed one as all the sets puts it at the same place. The second problem will be that the pair of cards is not just passthrough buffer, but contains a programmable interface. Adding several cards to a system would ressult in I/O conflicts. These I/O ports are used for example when the interface is initialized by the POST.

pearce_jj
August 17th, 2011, 12:09 AM
Interesting. So what about a hub-and-spoke configuration then?

lyonadmiral
August 18th, 2011, 05:23 PM
I just want to clarify, I do not mean daisy chain units together, but to put 3 units in using the slots on the 5150 motherboard.

pearce_jj
August 18th, 2011, 11:49 PM
Adding several cards to a system would ressult in I/O conflicts. These I/O ports are used for example when the interface is initialized by the POST.

I didn't see this part before for some reason - so it seems then the answer is no, as there is no way to control the ROM and port addresses used by the expansion unit set-up (see the expansion-unit manual (http://vintage-blog.peacon.co.uk/downloads/manuals/ibm-pc/IBM_Options_and_Adapters/vol1/expansion-unit/OA-IBM_Expansion_Unit_(5161).pdf), page 9).