using a 27C800 EPROM in an A600 for multiple KS

[kipper2k]

Hi All,

i am wondering about using a 1mb chip (27C800) in an A600 that contains 2 kickstarts, 1 in the upper and lower address area of the chip. I know the Xbox PLCC chips can be made to select high or low address areas for multiple OS's and wonder if the same can be achieved with a EPROM for the Amiga by holding an address line high etc. A one chip solution would be great with just a toggle switch.

Can this be done ?, any ideas anyone ?

Thanks

heres the datasheet... http://www.datasheetcatalog.com/data...8/27C800.shtml

[Secret Vampire]

I think I saw someone on ebay selling just such a solution a month or so back. I can't see why it wouldn't work, since the advice for using a 27c800 with a single ROM is to hold the high address bit low, a switch to select low/high (Or some logic to do it from the keyboard at startup, a-la the more expensive kickstart switchers) should let you flip ROMs within a single chip.

[Toni Wilen]

It works, but because A600 supports >512K ROMs you must not connect "extra" address bit(s) to ROM socket.

[kipper2k]

Thanks guys,

What i would like to do would be to use 2.05 as the low area KS and 3.1 as the upper KS.
I am assuming the process is to read my roms, and then byte swap them both, join the 2 images together with the 2.05 as the low address region, burn them to the 42 pin 27C800 and then this is where the guesswork comes into play...

Is it Q15-A1 (pin 31) that controls whether the upper or lower region is read by either holding it high or low ?

Thanks

[alexh]

Once you have KS3.1 on an A600 you never ever want or need to go back to 2.05.

The only think you might want is KS1.3 for compatibility with patch for IDE support.

http://www2.gup.jku.at/~tkoeck/kick1....device_patch/

[kipper2k]

Thanks Alex,

One of the main reeasons is i want the option of the early startup to control whether its Pal or NTSC, i know some games dont like KS 3.1 so thats why i want to do it this way so i can leave my options open and also get the one chip solution working so i can play around with the different ROMs

[alexh]

Originally Posted by kipper2k

One of the main reasons is i want the option of the early startup to control whether its Pal or NTSC

A nice feature of KS3.1, but games usually just reset it back to whatever they have been programmed to.

Originally Posted by kipper2k

i know some games dont like KS 3.1 so thats why i want to do it this way so i can leave my options open and also get the one chip solution working so i can play around with the different ROMs

In my experience there is little or no compatibility difference between 2.05 and 3.1!

You need KS1.3 for higher compatibility (which is why I mentioned it in my last post).

Plus are you not going to be playing the WHDload versions instead?

[kipper2k]

Hi Alex,

I have a 4GB CF card and pcmcia card installed on my 1200 with the indivision so i am happy to use that with my WHDload. I just like to use the a500 and A600 sometimes with the good old floppy drive. Using a CF card with the OS installed i find a little too slow for use on the A600. Even just loading the A-Z games listing is slow lol. I like it though for the true retro (albeit with a few little modifications).

Also a one chip mod iwould be better than a rom switcher in the sense that it would take up less room obviously in the A600 itself. Do you know which pin should be held high/low to address the upper/lower area of the chip

thanks

[alexh]

Originally Posted by kipper2k

Using a CF card with the OS installed i find a little too slow for use on the A600. Even just loading the A-Z games listing is slow lol. I like it though for the true retro (albeit with a few little modifications).

Use a better disk filesystem than FFS, add buffers to the disk, use icon.info files with less gfx, put fewer games in the same folder etc.

Originally Posted by kipper2k

Even just loading the A-Z games listing is slow lol.

Sounds like you are using a lame front end "game selector" tool.

Originally Posted by kipper2k

Do you know which pin should be held high/low to address the upper/lower area of the chip

The "highest" address pin of course.

[kipper2k]

Thanks Alex

Its tough to use the A600 on CF card after you get spoilt seeing it behave on an A1200, i'll tone down the colours etc like you say and see what the results are.


Thanks again

[kipper2k]

Originally Posted by alexh

Once you have KS3.1 on an A600 you never ever want or need to go back to 2.05.

The only think you might want is KS1.3 for compatibility with patch for IDE support.

http://www2.gup.jku.at/~tkoeck/kick1....device_patch/

If i wanted to just use a 1.3KS on an A600 can i just double up the 256K 1.3 rom, byte swap it and then burn to an eprom ? (assuming i dont care about patching the ide controller). I dont have the correct version of rom files that remus calls for to create a 512k file so it looks like this would be my only option


Thanks

[Doobrey]

Originally Posted by kipper2k

If i wanted to just use a 1.3KS on an A600 can i just double up the 256K 1.3 rom, byte swap it and then burn to an eprom ?

Yes.
The jump at the start of the first ROM image will make the CPU execute the code in the second image which is in the right address space (256KB ROMs are built with a base address of $FC0000)

BTW, What did ROMsplit say about your 1.3 ROM image?
Genuine 34.5 ROM images should work

[kipper2k]

Originally Posted by Doobrey

Yes.
The jump at the start of the first ROM image will make the CPU execute the code in the second image which is in the right address space (256KB ROMs are built with a base address of $FC0000)

BTW, What did ROMsplit say about your 1.3 ROM image?
Genuine 34.5 ROM images should work

Thanks Doobrey,

I should be getting the chips later on this week so i am waiting to get them before i sit down and play