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Re: Understanding a little something about bank-switched RAM

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On 2016-01-17 20:07:04 +0000, David Empson said:

> No, switching on the RAM (for read or write) affects D000-FFFF.
> 
> If you use locations C081-C083, you are read and/or write enabling bank
> 2 of $D000-$DFFF, plus all of $E000-$FFFF.
> 
> IF you use locations C089-C08B, you are read and/or write enabling bank
> 1 of $D000-$DFFF, plus all of $E000-$FFFF.
> 
> (C084-C087 are echos of C080-C083; C08C-C08F are echoes of C088-C08B.)

This combined with the map in the other message clears it up for me.

> If you want to read enable the RAM from the monitor while NOT running
> any operating system (e.g. just started up a //e with no disk in the
> drive, then Ctrl-Reset into BASIC), you can do so by copying the ROM
> into the language card RAM, then switch over to RAM. This results in the
> monitor code being able to continue without interruption.
> 
> This sequence should do the trick:
> 
> C081
> C081
> D000<D000.FFFFM
> C083

I didn't think to do that, but I understand completely.

> (For anyone else following along, this won't have the desired effect on
> a IIgs, which has the monitor code in a different bank, and the IIgs
> monitor has considerably different handling of memory banks.)

How about a IIc Plus? I ask because I have both a IIc Plus and a IIGS 
and the memory management on the IIGS struck me as different enough 
that I thought I should stay away when playing around.

I imagine if I don't boot into ProDOS, I can play around with the 
standard monitor and banks on the IIc Plus, no?

> With an original Apple ][ (or INTBASIC active in DOS 3.3), D000-DFFF
> comes before the Integer BASIC interpreter (which starts at $E000).
> D000-D7FF contains utility functions which can be CALLed from Integer
> BASIC, originally known as "Programmer's Aid #1", an optional ROM that
> could be installed in the D0 socket of an Apple ][ or a ROM card for an
> Apple ][+ which added Integer BASIC. I don't recall what is in D800-DFFF
> for INTBASIC - it was an empty socket in the Apple ][ or ROM card (I
> seem to recall a third party debugging tool which could be installed in
> that socket).

Thanks for this. I didn't know this history. :-)

>> I think I've learned that when you switch to reading RAM, you're
>> actually switching to read all of the regions that are bank-switchable,
>> not just D000-DFFF.
> 
> Correct.
> 
> The whole 12K address space is switched with the read or write soft
> switches.
> 
> The bank 1/2 selection only affects which bank is active in the
> D000-DFFF area. The E000-FFFF area is the same for both banks.

Wonderful! Thank you. Thank you. Thank you!

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Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-16 21:08 -0600
  Re: Understanding a little something about bank-switched RAM dempson@actrix.gen.nz (David Empson) - 2016-01-17 18:54 +1300
    Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-17 11:38 -0600
      Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-17 11:39 -0600
      Re: Understanding a little something about bank-switched RAM dempson@actrix.gen.nz (David Empson) - 2016-01-18 09:07 +1300
        Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-17 16:18 -0600
          Re: Understanding a little something about bank-switched RAM dempson@actrix.gen.nz (David Empson) - 2016-01-18 15:42 +1300
            Re: Understanding a little something about bank-switched RAM "Bill Garber" <willy46pa@comcast.net> - 2016-01-17 22:27 -0500
              Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-18 10:53 -0600
            Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-18 10:50 -0600
          Re: Understanding a little something about bank-switched RAM michael.pohoreski@gmail.com - 2016-01-18 09:40 -0800
            Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-18 17:23 -0600
              Re: Understanding a little something about bank-switched RAM michael.pohoreski@gmail.com - 2016-01-19 23:05 -0800
                Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-20 10:06 -0600
  Re: Understanding a little something about bank-switched RAM michael.pohoreski@gmail.com - 2016-01-17 05:09 -0800
    Re: Understanding a little something about bank-switched RAM ultramagnus_tcv <mikew@thecomputervalet.com> - 2016-01-17 18:36 -0600
  Re: Understanding a little something about bank-switched RAM "Bill Garber" <willy46pa@comcast.net> - 2016-01-17 11:45 -0500
    Re: Understanding a little something about bank-switched RAM dempson@actrix.gen.nz (David Empson) - 2016-01-18 09:07 +1300
      Re: Understanding a little something about bank-switched RAM "Bill Garber" <willy46pa@comcast.net> - 2016-01-17 15:33 -0500
      Re: Understanding a little something about bank-switched RAM michael.pohoreski@gmail.com - 2016-01-18 09:30 -0800
        Re: Understanding a little something about bank-switched RAM dempson@actrix.gen.nz (David Empson) - 2016-01-20 18:17 +1300

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