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Model B+ Disc Interface

Posted: Thu Dec 28, 2017 11:14 am
by Coeus
I gather the B+ in both 64k and 128k versions used the 1770 for the disc interface but sis this come factory installed on these models or was it an upgrade option?

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 11:53 am
by Pernod
Not sure why this is in emulators, but the 1770 in the B+ models was factory installed.

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 12:13 pm
by Coeus
Pernod wrote:Not sure why this is in emulators, but the 1770 in the B+ models was factory installed.
Thanks. I did wonder about posting it in hardware but the reason for the question was whether to emulate a B+ without the 1770 so the answer to that is "No".

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 1:19 pm
by SteveBagley
Doesn’t the B+ motherboard support both the 8271 and the 1770? Also, I think the B+ motherboard was used in a few other places without either (Acorn X.25 gateway?)…

Steve

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 1:27 pm
by CMcDougall
Not all B+ had a factory fitted 1770.
These were bought as kits, first with DFS2.0j which was crap, then 2.26 , hence mine now plays working discs correctly without stupid errors :D

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 2:00 pm
by Pernod
SteveBagley wrote:Doesn’t the B+ motherboard support both the 8271 and the 1770? Also, I think the B+ motherboard was used in a few other places without either (Acorn X.25 gateway?)…
There are markings on the board for a 8271 but was never implemented. And yes the X.25 Gateway did use the B+ board without the 1770.
CMcDougall wrote:Not all B+ had a factory fitted 1770.
These were bought as kits, first with DFS2.0j which was crap, then 2.26 , hence mine now plays working discs correctly without stupid errors :D
Really? I wasn't aware of that.

Also be aware that not all Masters had the 1770 either, the Master ET didn't have it fitted.

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 4:04 pm
by crj
Something I've always wondered...

The trick of laying out 8271 and 1770 disc interface circuits overlapping in the same circuit board area always struck me as particularly nifty, but did the 8271 circuit actually work? Has anybody ever tried fitting an 8271 to a B+?

I'm guessing there might at least have been some lurking deep in the bowels of Acorn R&D early in development, so they could get stuff done before the 1770 DFS was ready.

(The other thing I've always wondered is why on earth they didn't bring out all the signals they needed on the expansion header. It seems bizarre that the B+128 needed flying leads like some third-party add-on.)

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 4:22 pm
by Coeus
It makes me wonder what they were thinking. I know hindsight is a wonderful thing and it is easy for us to say now that backing the 8271 in the first place was a mistake but why continue even after that has become apparent? Where they concerned about software compatibility for games that drove the controller directly? Or did the development of B+ start even before 3rd parties had introduced various 1770 upgrades? Or was it a case of "not invented here syndrome" that prevented them from simply licensing a 1770 DFS from one of the others.

Re: Model B+ Disc Interface

Posted: Thu Dec 28, 2017 4:38 pm
by CMcDougall
8271 was inshort supply /scarce / too expensive due to low supply high price

plus by 1985 ADFS was out, & 8271 would not handle that

plus the B+OS was not compatible with OS1.2 , so games never worked anyways like M128 OS3.2 /3.5