[Simh] SDS Card Reader

[kenr]

I'm interested in using the SDS 940 simulator to run programs from the 
XDS PAL tapes found on bitsavers.
Most of these programs were loaded onto the PAL library tapes from 
punched cards by SDS/XDS in a self loading format for distribution to 
customers.  Customers would copy the files from tape onto punched 
cards.  The self loading programs assume a card reader, not a paper tape 
or mag tape.

The SDS 940 simulator does not have a card reader driver so  I have a 
couple of questions.

1. Why isn't there a card driver for the 940?
2. I notice simulators for similar machines also don't have card 
drivers,  why is that?
3. Does anyone know of a (maybe unfinished, unofficial) card driver that 
I might use?
4.  Where might one find the developer documentation mentioned in the 
simh faq?

Anyone care to answer these or offer an opinion on driver development?

Ken