MultiBIOS install with Single Switch?

[hellbelly]

Hi


Now that Arakons MultiBIOS is available to download I've decided I've got to try it out! I've been trying to figure out if it would be possible to install it and be able to select the region by using a single 3 position on-off-on kind of switch?


I've spent ages trying figure it out on paper but can't get it sorted, but I am an amateur at this! I don't have any chips to program yet so it's all theory at the moment.


Is it possible? Has anyone done it?


Thanks in advance for any advice.


Cheerio

Pete

 

[ExCyber]

I haven't done the math, but it seems like it would work to connect the center terminals to ground through a sufficiently large resistance to create a "default".

 

[cgfm2]

Now that Arakons MultiBIOS is available to download I've decided I've got to try it out! I've been trying to figure out if it would be possible to install it and be able to select the region by using a single 3 position on-off-on kind of switch?

From what I saw the multibios with two switches has four possible switch settings (off-off, off-on, on-off, on-on) and with a three position switch you would get at most three settings.

The least complex configuration I can think of is:

Switch left terminal = BIOS pin 38, and a 4.7K ohm resistor to +5V

Switch middle terminal = Ground

Switch right terminal = BIOS pin 39, and a 4.7K ohm resistor to +5V

In one of the ON positions, the switch will connect pin 38 to ground, overriding the pull-up. Pin 39 will be pulled high. This is reversed for the other ON position (pin 38 high, pin 39 low)

In the center position both pins will be pulled high. The only setting you can't get is with both pins low.

You can always split the BIOS into four parts and re-order them as needed based on the switch settings before you write it to an EPROM. To map the three BIOS images you need to the three available switch settings.

I don't know anything about the multibios in particular, I assume we are just toggling the high-order address lines of a 27C4096 to select a 128K chunk. So no guarantees.

 

[ExCyber]

I assume we are just toggling the high-order address lines of a 27C4096 to select a 128K chunk.

You assume correctly.


I think Arakon's instructions are for all 4 positions because he shipped some chips with a bonus in the extra position, but in general it's unnecessary.

 

[hellbelly]

Many thanks for the replies, I have some info from Arakon also and will try it out when I get the console

Pete