[sebhc] ET-3400: Why missing pins on 40 pin expansion connector?

[Whipaway]

Hello.
Is there any reason that front row pins 1 and 2  and rear row pins 3,4,6,7,8,,9,10,15 are omitted from the 40 pin expansion connector on the ET-3400A:? (And ET-3400 after modification) 
Also, why are the RE and Clock2 signals available on 2 pins each (Isn't one pin enough?)
Are the equivalent pins that are omitted on the ETA-3400A / EWA-3400A connected to anything?
The reason I am asking is that I would like to have all signals available for prototyping / experimentation, but do not wnt to cause problems if I ever get an ETA-3400A / EWA-3400A accessory and want to plug everything together, and having the RE and Clock2 signals on one pin each instead of two would free up two pins for the possibility of adding other signals to the bus (such as Line or 1Hz signals?)
Also, does anyone have a schematic for the ETA-3400A / EWA-3400A?
I would like to attempt to build one myself.
Thanks,
Paul Kowal
whipaway at yahoo.com

       
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