Can I put an 800XL OS in a 1200XL without replacing MMU?

[ACML]

I just want the 600/800XL OS, but don't want to replace the MMU. Actually, I want to retain the L1 and L2 LED and F1-4 functionality of the 1200XL. If I put in a 800 XL OS split on two 2764s (8K) will I have to press SELECT even though there is no internal BASIC? I thought someone said that the machine will still disable the 8K block as if the cartridge was there if you don't press the SELECT key. Or is this only an issue if I replace the MMU or have 16K ROM capability. Again, I'm not using the 16K ROM on one chip. I'm keeping the 1200XL convention of putting the 16K OS on two 8K 28 pin 2764 eproms. Again, is pressing SELECT needed on boot up if I want all 64K? Thanks!

Edited October 6, 2013 by ACML

[Rybags]

I believe if you split into 2 8K images on seperate ICs then you should be able to retain the 1200XL MMU. Unlike 800XL the 1200XL has seperate chip selects depending on what part of the OS you're accessing.

 

Press "Select" - that's something only for XEGS and some custom OSes. If referring to "Option" then no, holding it on startup won't make a difference to the running of Basic on cartridge. On stock machine, a standard cart will always take precedence over Ram/Rom switching in that area.

 

"All 64K" - like other 64K machines you in fact can only get to 62K, the 2K where the I/O chips are addressed can't access the Ram underneath.

[candle]

yes you can

if you know what wired-or means

[ACML]

I believe if you split into 2 8K images on seperate ICs then you should be able to retain the 1200XL MMU. Unlike 800XL the 1200XL has seperate chip selects depending on what part of the OS you're accessing.

 

Press "Select" - that's something only for XEGS and some custom OSes. If referring to "Option" then no, holding it on startup won't make a difference to the running of Basic on cartridge. On stock machine, a standard cart will always take precedence over Ram/Rom switching in that area.

 

"All 64K" - like other 64K machines you in fact can only get to 62K, the 2K where the I/O chips are addressed can't access the Ram underneath.

Thanks for the reply. Yes, I meant OPTION, not SELECT. I'ts been a long time since I've had an 800XL. I just wanted to make sure that by not pressing the OPTION on start up, the OS doesn't reserve the 8K block for internal BASIC that an 800XL would have. I'm actually putting in two 27128's with the 800XL and 400/800 OSB operating systems on it. Since I upgraded the video with the ClearPic 2 mod, I'm using the existing RF 2/3 channel select as the OS selector.

[oracle_jedi]

Adding the 800XL OS and MMU to a 1200XL does not disable the F1-F4 keys, the L1/L2 LED flash, nor does it require you to hold OPTION on startup.

 

Pin 18 of the MMU is what controls the need to hold OPTION, and unless you connect it to pin 11 of the PIA, the 1200XL will continue to boot up with as if you held OPTION down on an 800XL.

 

The F1-F4 keys work under the XL OS.

 

The LED lights will work unless you install a 256K memory expansion which uses those pins of the PIA for memory bank control.

[flashjazzcat]

Ignore...

Edited October 7, 2013 by flashjazzcat