BBC B Issue 3 O.S. 1.0

[e668ecp]

The old BBC that i've fixed the memory fault on has O.S. 1.0 mounted on a daughter board as two chips, LO and HI; see image. I've never seen this before.

I'e tried swapping the daughter board / basic roms for later versions but the BBC refuses to start.

Can it be done, if so how?

[IanB]

OS 1.00 on the butterfly board was shipped with the early disc upgrade kits and upgrading to the OS1.20 ROM should be just a simple swap with no changes required.

However, the early versions of the butterfly boards had thick pins that plugged into the BBC's OS ROM socket and that damaged the socket so a normal ROM wouldn't work and you had to replace the OS ROM socket to fix it so that might be your problem. Later versions of the butterfly board had turned pin extensions that didn't damage the BBC OS socket.

[tricky]

Maybe not damage, but stretch
Still, if you have one, you could try your new ROM in a turned pin socket in the old socket.

[e668ecp]

Bingo! I'd not thought of that, is the OS 1.2 rom available as an SSD?

[flaxcottage]

Here: - http://www.flaxcottage.com/BBC_ROMS/Default.asp

[Bobbi]

How do the MOS versions line up with the board issue numbers, out of curiousity?

What would be the original MOS for a issue 3?

[flaxcottage]

My original Issue 3 came with OS 0.1 in ROM.

[Bobbi]

What versions exist? Just 0.1, 1.0 and 1.2?

[1024MAK]

Most are here

Mark

[Bobbi]

Am I correct in believing 1.2 is the most recent that works in a Model B?

[1024MAK]

Yes.

[jgharston]

No.

OS 1.23 works in a BBC B.

And there's an OS 1.5x floating around somewhere.

OS 2.xx will work in a BBC B, but will be unable to access the shadow screen.

[JasonStonier]

OS 1.23 works in a BBC B.

Is there any advantage to putting OS1.23 in a B?

[1024MAK]

OS 1.23 works in a BBC B.

Is there any advantage to putting OS1.23 in a B?

It will make fault finding more difficult if you suffer from a DRAM chip failure...

Mark

[Bobbi]

How so? I am curious.

[1024MAK]

How so? I am curious.

See the changes text which says that it assumes 32k bytes of RAM. OS 1.20 (Acorn’s last mainstream version for Model A and Model B machines) tries to work out if it’s running on a 16k or 32k RAM machine and posts the appropriate message. By trying different positions of link S25, it’s possible to select which bank of 16k DRAM chips is used for the 0x0000 to 0x3FFF part of the 6502 memory map. If there is good working RAM in this area, the machine will start up as a working 16k machine (as if it was a Model A).

Mark

[Bobbi]

Ah, good to know! Thanks!

[daveejhitchins]

Well, that's an easy fix . . . If you have problems: swap the ROM back to the earlier version

Dave H.