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Groups > comp.sys.apple2.programmer > #1477

Method to address both Legend and Saturn RAM cards

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After looking at the technical documentation for the Legend 64KC and the
Saturn 32/64/128K RAM cards, it seems that one could write a common routine
using 6502 indexed addressing to work on both models of RAM card.

The Legend 64KC provides a bank select address at location $C084. This is a
write only address used to select bank 0 through 3.

The Saturn RAM cards use a series of addresses to select a bank, starting
with $C084 for bank 0, $C085 for bank 1, $C086 for bank 2, and so on.

So it seems to me that we could use indexed addressing with the X register
and $C084 as the base address. First we should have an earlier subroutine
detect which card is installed, or just ask the user, and store the setting
in ZP location. The subroutine to select a bank should accept the bank
number in the X-reg.

Here's my first naive attempt at writing the routine. There's definitely
room for improvement, but this is the general idea:



BANKBASE	EQU	$C084	; BASE ADDRESS FOR BANK SELECT ADDR
RAMTYPE		EQU	$06	; TYPE OF RAM CARD INSTALLED
*
*
* SELECT A 16K RAM BANK. DESIRED BANK NUMBER
* SHOULD BE PASSED IN THE A-REG.
*
BANKSEL
		LDA	RAMTYPE	; WHAT TYPE OF RAM CARD?
		BEQ	:LEGEND	; 0 = LEGEND, 1 = SATURN
		TAX
		STA	BANKBASE,X	; SELECT BANK
		RTS
:LEGEND		LDX	#0
		STA	BANKBASE,X	; SELECT BANK
		RTS



Documentation:

<http://lostclassics.apple2.info/wp-content/files/Legend/64KC.pdf>
<http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Interface%20Cards/Memory/Saturn%20Systems%20RAM%20Board/Manuals/Saturn%20Systems%2064K%20and%20128K%20RAM%20Board%20-%20Operations%20Manual.pdf>

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Method to address both Legend and Saturn RAM cards D Finnigan <dog_cow@macgui.com> - 2015-01-15 19:09 +0000
  Re: Method to address both Legend and Saturn RAM cards "Anton Treuenfels" <teamtempest@yahoo.com> - 2015-01-15 22:21 -0600
    Re: Method to address both Legend and Saturn RAM cards gids.rs@sasktel.net - 2015-01-16 09:41 -0800
      Re: Method to address both Legend and Saturn RAM cards D Finnigan <dog_cow@macgui.com> - 2015-01-16 19:08 +0000
      Re: Method to address both Legend and Saturn RAM cards qkumba <peter.ferrie@gmail.com> - 2015-01-17 21:32 -0800
        Re: Method to address both Legend and Saturn RAM cards gids.rs@sasktel.net - 2015-01-17 22:33 -0800
          Re: Method to address both Legend and Saturn RAM cards gids.rs@sasktel.net - 2015-01-17 22:54 -0800
            Re: Method to address both Legend and Saturn RAM cards Leandro Polimeno <leandro.polimeno@gmail.com> - 2015-02-10 04:53 -0800
              Re: Method to address both Legend and Saturn RAM cards gids.rs@sasktel.net - 2015-02-10 21:19 -0800
                Re: Method to address both Legend and Saturn RAM cards Leandro Polimeno <leandro.polimeno@gmail.com> - 2015-02-11 05:22 -0800
          Re: Method to address both Legend and Saturn RAM cards D Finnigan <dog_cow@macgui.com> - 2015-01-18 10:09 +0000
            Re: Method to address both Legend and Saturn RAM cards "Anton Treuenfels" <teamtempest@yahoo.com> - 2015-01-19 08:33 -0600
              Re: Method to address both Legend and Saturn RAM cards D Finnigan <dog_cow@macgui.com> - 2015-01-19 18:29 +0000
              Re: Method to address both Legend and Saturn RAM cards qkumba <peter.ferrie@gmail.com> - 2015-01-20 09:33 -0800
                Re: Method to address both Legend and Saturn RAM cards "Anton Treuenfels" <teamtempest@yahoo.com> - 2015-01-20 17:06 -0600

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