blochowi@rt3.cs.wisc.edu (Jason Blochowiak) (11/13/89)
In article <2190.cortland.info-apple@pro-houston> jabernathy@pro-houston.cts.com (Joe Abernathy) writes: >The FPE employs a 16-bit data bus. "Employs"? I haven't even seen the FPE, much less any spec sheets for it, but... Unless I'm totally confused as to the //gs' design, it has an 8 bit data bus, and a 16 bit address bus. The 24 bit addressing is generated by sticking the bank number (the upper 8 bits of the 24 bit address) onto the data bus at the right time. So, what this means (I'm assuming here that I'm not totally lost, and I don't think I am) is that the FPE can talk to itself in whatever fashion it likes (it could have a 128 bit data bus, for all the external world cares), but it can only communicate with the //gs in discrete 8 bit chunks. Perhaps they've done something to make it look a little bit more like 16 bits, possibly by grouping the I/O space addresses into words and combining the the buffered values stored into the I/O space, but that still doesn't get away from the fact that the //gs can only give it 1 byte at a time. If I'm wrong, I'd really like to hear about it, as it'd kind of change things for this hardware project I'm working on - besides, Apple would probably be interesting in knowing that their hardware manual for the //gs is, at the very least, quite misleading. >INET: jabernathy@pro-houston.cts.com -- Jason Blochowiak - blochowi@garfield.cs.wisc.edu or jason@madnix.uucp "Education, like neurosis, begins at home." - Milton R. Sapirstein