Re: [stella] smart multicart

Subject: Re: [stella] smart multicart
From: Piero Cavina <p.cavina@xxxxxxxxxxxxx>
Date: Mon, 25 Aug 1997 22:44:36 +0100
>Date: Mon, 25 Aug 1997 13:59:03 -0400
>From: danboris@xxxxxxxxxxxxxxxx (Dan Boris)
>To: p.cavina@xxxxxxxxxxxxx
>Subject: Re: [stella] smart multicart
>X-Sun-Charset: US-ASCII
>> From owner-stella@xxxxxxxxxxx Mon Aug 25 12:33 EDT 1997
>> X-Sender: cvnp06k1@xxxxxxxxxxxxx
>> Mime-Version: 1.0
>> To: stella@xxxxxxxxxxx
>> Subject: Re: [stella] smart multicart
>> Sender: owner-stella@xxxxxxxxxxx
>> X-Lines: 41
>> Ok, now I have this thing in mind... please forgive me if it's a crap idea,
>> I know just a little of electronics.
>> Could a joystick port be used to switch banks of Rom memory? (remember that
>> the joystick ports can be set for output.)
>> Imagine a cart with a 64K Eprom, address lines 0-11 go to the VCS, and
>> 12-15 to a DB9 connector plugged into the Player 2 joystick port (some
>> pull-down resistors could be needed).
>> Each 4K bank would begin with the code to switch to the first bank (for
>> bankswitched games), or to the bank with the game select menu (for a multi
>> cart use). The VCS would switch banks writing to the register that controls
>> the pins of the player 2 joystick port.
>> Pros: minimum extra hardware needed
>> Cons: you lose one joystick port :)
>> Is this a totally inpracticable idea?
>The problem with this is that as soon a the game you selected started, it
>would initilize the joystick ports and you would loose your bank select
>signals. The other problem is that once you have selected a bank you need
>a way to restart the game.
>The first problem could be solved by latching the bank number and not
>allowing it to be changed once it is latched. The other problem is a
>little trickier. You would have to prevent the new bank number from
>becoming active until your code could do a JMP ($FFFC). You could build a
>circuit to enable the new bank number as soon as it sees a read from $FFFC
>Can anyone else think of an easier way?
>						Dan Boris

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