Date   : Wed, 26 Sep 2001 09:11:37 -0500
From   : "Gordon Jefferyes" <gordon-j@...>
Subject: Re: BBC B+ 128 question.

Hi,

The difference between the BBC B and B+ 128K
that stops most of the games from working is actually
NOY the extra memory as this memory really is just a memory extension
upgrade.
The true problem is the fact that a lot of games require the
original BBC B OS1.2 to work.
The reason this is the case is that many games cheated and
jumped directly to addresses in the BBC B operating system.
They did this to get a little extra speed out of the game instead
of jumping into the OS through a 'legal' entry point.
The simple problem is that if you change the code in the OS
as happened in the BBC B+ OS these illegal OS calls will
fail as they are now jumping to the wrong bit of code.

The best thing to do is to get an EPROM with OS1.2 on it
and plug it into your BBC B+, instead of the BBC B+ OS

I did this to a friends machine a long long time ago by
getting a BBC B OS EPROM soldering another socket on top
of it and plugging the BBC B+ OS on top of that, then I added
a switch on the chip select lines and some pull up resistors
so that the two OS's could be switched between.

(Note also that the BBC B+ OS chip also contained the BASIC
ROM so you also need another copy of BBC BASIC in one
of the other rom sockets for this to work, or you need a 32K EPROM
with both the BBC B OS and the BBC Basic)

Doing this really does make the machine believe it is a BBC B
with only the 32K of ram, and every game we then tried
worked correctly.


GordonJ
http://mess.emuverse.com
http://mamerominfo.retrogames.com




----- Original Message -----
From: "Victor Rozanov" <vic792r@...>
To: <bbc-micro@...>
Sent: Tuesday, September 25, 2001 03:07
Subject: [BBC-Micro] BBC B+ 128 question.


>
> Hello,
>
> I have BBC B+ with 128k of ram, OS 2.0
> DFS 1770 2.22
> Also I have ADFS rom but by some reasons
> it does not work with the floppy disk drives.
> It looks like it can only work with the winchester
> drive. I do not know what this edition  of ADFS is so I puled it out
> and now I  only have two ROMs 32k - Basic and OS and 16k - DFS.
> My problem is I can not start most of the games on this machine.
> Sometimes it even says " you need the original acorn hardware" or
> something like that. Most of the times the games just hang and the
> machine freze. You have to do the hard reset after that. I tried
> the same game titles in the emulator ( beebem ) they work fine.
> I know that the memory alocation is different for B and B+
> And it has the special registers to manage sideways RAMs and
> 64K of main and shadow ram but I can not find complete manual
> describing the memory issues anywhere on BBC lives or 8BS.
> May be you can tell me where I can read more about the memory
> on B+ 128.  For now my goal is at least to find the way to
> turn B+ into B with 32k for starting all the games with no
> problems.
> I would really appreciate if you can help me with that.
> What is the trick? Do I need to change something in hardware?
>
> Thank you.
> Best Regards.
>
> Victor.
>
>
>
>
>
>
>