csajp@its63b.ed.ac.uk (ECTU07 A Paxton CS) (01/21/87)
Having enough knowledge of hardware only to zarq thinks up, Could anyone
tell me the specs for the expansion port on an 800xl ?
( The one on the back where the pcb sticks out , he means). Please flame
constructively, I'm new to posting stuff.
I am here--> Alan Paxton. CS dept. University of Edinburgh
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Alan ]jhs@MITRE-BEDFORD.ARPA.UUCP (01/24/87)
The expansion port is basically a direct connection to the 6502 processor bus. A couple of additional signals are also present, like cassette audio in/out (?). There is also a line called "External Select" which has to do with whether external devices or ones in the Atari console get the bus. I am not certain how this works but suspect that it is supposed to be generated in the external device to let it pre-empt the bus when it feels like it. That would seem to give the best flexibility for expansion. Mapping The Atari, 1985 edition, contains a fairly complete description of the pinouts in one of the appendices. Note that the connector is a perfectly standard 50-pin card-edge connector, but the pin numbering used by Atari and reproduced in Mapping... is not standard. So be careful with pin numbering, especially if you use a standard connector instead of one purchased from Atari. The relationship between the two numbering schemes is simple, so there is no problem using a standard connector and making the translation. I am not at home now so don't have detailed information readily at hand. -John Sangster jhs@mitre-bedford.arpa