Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uwm.edu!ogicse!pdxgate!eecs!bairds
From: bairds@eecs.cs.pdx.edu (Shawn L. Baird)
Newsgroups: comp.sys.amiga.programmer
Subject: Direct hardware drive access
Message-ID: <2159@pdxgate.UUCP>
Date: 31 Mar 91 12:37:46 GMT
Sender: news@pdxgate.UUCP
Lines: 21

Well, after examining the CIA specifications in appendix F of the Hardware
Reference Manual, I found a small misprint in Chapter 10, "Interface
Hardware", of the Hardware Reference Manual. On page 238 it says:

     Bits labeled "PB" are output bits located in CIAAPRB ($BFD100).
                                                  ^^^^^^^

This should be CIABPRB, for which the correct address is given. Upon
switching to this register and using tips provided by Randell Jesup, I
was able to get the motor to come on and the drive to spin (Hey, it's
more excitement than I've had in weeks!). Thanks both to Mike Schwartz
and Randell Jesup for their help.

Note: Even the top of this page says CIAAPRA/CIABPRB. In fact, everything
else says CIABPRB. Why I saw only the one little reference to CIAAPRA I
don't know, but I guess it seemed to make sense that the registers for
controlling and sensing the disk would be on the same CIA chip.

---
 Shawn L. Baird, bairds@eecs.ee.pdx.edu, Wraith on DikuMUD
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