Path: utzoo!yunexus!ists!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!intercon!amanda@intercon.com From: amanda@intercon.com (Amanda Walker) Newsgroups: comp.sys.mac.programmer Subject: Re: 8530 SCC access Message-ID: <1553@intercon.com> Date: 16 Nov 89 02:41:16 GMT Article-I.D.: intercon.1553 References: <2571@ucsfcca.ucsf.edu> <2573@ucsfcca.ucsf.edu> Sender: news@intercon.com Reply-To: amanda@intercon.com (Amanda Walker) Organization: InterCon Systems Corporation Lines: 19 In article <2573@ucsfcca.ucsf.edu>, rampil@cca.ucsf.edu (Ira Rampil) writes: > IM uses 'strange' names (not Zilog) for these > registers, though it seems clear that READ CTL is (Zilog) RR8. I need > access to several of the Zilog registers ( there are more than 40!). Take another look at your Zilog databook. The SCC uses a register- pointer scheme to minimize the number of I/O addresses it takes up on the host's address bus. For example, to write to any register beside WR0, you write the register number into the control port for the channel you want, and then the next write done to the data port for that channel will be routed to the appropriate SCC register. Reading works in a similar way. This is how the SCC was designed; it's not a result of the Macintosh I/O architecture. On the Mac, the host addresses are different for reads and writes, so you need to add the appropriate offsets for the A & Bcommand & data ports to the read or write base addresses, but aside from that, using the SCC from the Mac is quite straightforward. Amanda Walker --