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Decoder board for Atari ST(fm)
Posted: 14 Dec 2020 20:45
by zChris
Since we now have a "Noob questions" section i will start it off.
My question is what really are a Decoder board for Atari ST(fm) ? I thought at first it was for using dual toses. But now im leaning on that it might be used mostly to get TOS2.06 working on a ST?
/zChris
Re: Decoder board for Atari ST(fm)
Posted: 14 Dec 2020 20:57
by Icky
@zChris
An STFM GLUE chip has the ROM address set at FC0000 so an STFM is stuck with using the 1.02 and 1.04 versions of TOS.
It is not so easy for it to use TOS 2.06 as this was built for the STE and its ROM address is E00000
So if you want to be able to boot TOS 2.06 you need a decoder that helps to bypass the GLUE chip looking for the FC0000 address but instead to look for TOS at E00000.
Re: Decoder board for Atari ST(fm)
Posted: 14 Dec 2020 20:58
by exxos
Decoder boards is like the ones I produce
https://www.exxosforum.co.uk/forum/viewt ... =16&t=2751
My boards will decode TOS 104 to TOS206 (you cannot use higher than TOS104 on a stock STFM)
DUALTOS is when you have a new ROM board like this one
https://www.exxosforum.co.uk/forum/viewt ... f=16&t=272 Where you can store 2 versions of TOS in the ROM. Selection is by a jumper on the ROM adapter PCB.
So you can have DUALTOS with TOS102 & TOS104 without a decoder board. Or TOS104 & TOS206 with a decoder board.