Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.sys.apple2.programmer > #5552

Re: Phantom reads on 6502, 65C02 and 65816

Show all headers | View raw

In article <sMKdnRMP4u1FhCnDnZ2dnUU7-T_NnZ2d@giganews.com>,
Kent Dickey <kegs@provalid.com> wrote:
>
>What's confusing is there are some models of 65c02 which may have a fix for
>some of this behavior.  Those 65c02's were generally not used in Apples (since
>they mess up RWTS).  I suppose it's possible they were used in the Apple IIc
>or IIc+ since those models moved to the IWM which could be more forgiving
>of these bus accesses (and had no slots, so didn't require strict Disk II
>compatibility).

I realized I didn't phrase the above properly--I have no idea if 65c02s with
fixes for the phantom cycles were used in Apple IIs.  But we know Apple pushed
WDC to put phantom cycles back into the 65816.  I don't know if 65c02's
with the fixes for these phantom cycles were used in Apple IIs, and I'm
speculating on the IIc/IIc+ and whether IWM doesn't need the phantom cycles.

I know the Apple //e went through at least 3 versions early on:
- unenhanced (6502) without Dbl-hires.  There was a free upgrade for this.
- unenhanced (6502), with Dbl-hires:  I know all about this one, I owned one.
- enhanced (65c02 of some sort), with Dbl-hires.  I never personally used this.

So it's possible some Apple IIs use a 65c02 with fixes for the phantom
cycles.  But it's also possible only early enhanced units did so, and Apple
changed to the WDC 65c02 which purposefully went back to the 6502 behavior.
I don't know of a good way to figure this out--if people test Apple //e's of
various ages, we could figure out the 65c02 type and if Apple changed
vendors.  I think the likely case is there are a number of Apple //e's with
65c02 with the phantom cycle fixes, but that Apple moved to the 65c02's with
the phantom cycles.

One thing that's very likely--various people put every type of 65c02 in
their Apples since it was pretty easy to change the CPU.  If you want
compatibility, you should assume phantom cycles and non-phantom cycles,
and code defensively.

I also didn't look up precisely what's the problem with RWTS and why it
needs the phantom cycles.  My speculation is when switching to
write mode, the disk drive may have needed the phantom read before the
first write to $C08F,X for it to work right when rewriting a sector.

Kent

Back to comp.sys.apple2.programmer | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Phantom reads on 6502, 65C02 and 65816 ol.sc@web.de (Oliver Schmidt) - 2020-05-06 17:04 +0000
  Re: Phantom reads on 6502, 65C02 and 65816 Andy McFadden <thefadden@gmail.com> - 2020-05-06 17:20 -0700
    Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-06 21:15 -0700
      Re: Phantom reads on 6502, 65C02 and 65816 Antoine Vignau <ntn.vignau@gmail.com> - 2020-05-06 23:29 -0700
        Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-07 01:20 -0700
      Re: Phantom reads on 6502, 65C02 and 65816 ol.sc@web.de (Oliver Schmidt) - 2020-05-07 09:33 +0000
        Re: Phantom reads on 6502, 65C02 and 65816 TomCh <tomcharlesworth26@gmail.com> - 2020-05-07 04:48 -0700
          Re: Phantom reads on 6502, 65C02 and 65816 ol.sc@web.de (Oliver Schmidt) - 2020-05-07 12:33 +0000
            Re: Phantom reads on 6502, 65C02 and 65816 kegs@provalid.com (Kent Dickey) - 2020-05-07 09:23 -0500
              Re: Phantom reads on 6502, 65C02 and 65816 Andy McFadden <thefadden@gmail.com> - 2020-05-07 10:02 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Andy McFadden <thefadden@gmail.com> - 2020-05-07 11:27 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Antoine Vignau <ntn.vignau@gmail.com> - 2020-05-07 12:25 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Andy McFadden <thefadden@gmail.com> - 2020-05-16 19:05 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-18 06:09 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Andy McFadden <thefadden@gmail.com> - 2020-05-26 07:42 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-27 00:04 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 Anthony Lawther <alawther@spammenot.mac.com> - 2020-05-09 07:54 +0900
              Re: Phantom reads on 6502, 65C02 and 65816 ol.sc@web.de (Oliver Schmidt) - 2020-05-07 19:28 +0000
              Re: Phantom reads on 6502, 65C02 and 65816 kegs@provalid.com (Kent Dickey) - 2020-05-07 15:16 -0500
                Re: Phantom reads on 6502, 65C02 and 65816 Antoine Vignau <ntn.vignau@gmail.com> - 2020-05-07 15:07 -0700
                Re: Phantom reads on 6502, 65C02 and 65816 kegs@provalid.com (Kent Dickey) - 2020-05-07 19:48 -0500
                Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-07 18:46 -0700
        Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-07 08:32 -0700
          Re: Phantom reads on 6502, 65C02 and 65816 ol.sc@web.de (Oliver Schmidt) - 2020-05-07 19:36 +0000
          Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-07 23:39 -0700
            Re: Phantom reads on 6502, 65C02 and 65816 Antoine Vignau <ntn.vignau@gmail.com> - 2020-05-08 01:20 -0700
              Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-08 01:41 -0700
            Re: Phantom reads on 6502, 65C02 and 65816 Nick Westgate <nick.westgate@gmail.com> - 2020-05-08 05:46 -0700

csiph-web