A National Semiconductor Multibus I floppy controller

[Jon Hales]

Browsing Bill's intel_devel drive, I was reminded of Herb's useful Intel_FDC_field_guide.txt. The last line of Herb's file refers to "National Semiconductor BLC-8201 replaces SBC-201".

National Semiconductor also made a BLC8222 controller which supported FM and MFM and 8" and 5¼" drives. I came across one on eBay.co.uk. 

The documentation - copied to intel_devel\Jon\NatSemi_BLS8222 - consists of:

- photographs of component and solder sides of the board

- dumps of the two 2716 EPROMs (with a checksum as the filename)

- several PDFs: a 3-page datasheet, a note about jumpers and a set of schematics.

There may be further information in Nat Semi databooks of the early 1980s.

National Semiconductor were one of the manufacturers of IEEE-796 Multibus-based systems. There's no reason to suppose the original drivers for the board would have supported the BLC8222 in an Intel MDS under Intel's OS.

I haven't learned about the OS used with Nat Semi systems of that period. Can anyone share what they know?

Regards

Jon

[roger arrick]

DANG, I been looking for one of those for years!

And WITH DOCS and BOX!!

It's suppose to emulate having both 201 and 202 in the same system.

Congrats with envy! 🙂

-Roger in TX

---

From: intel-...@googlegroups.com <intel-...@googlegroups.com> on behalf of Jon Hales <jonh...@gmail.com>
Sent: Monday, September 4, 2023 7:42 AM
To: intel-...@googlegroups.com <intel-...@googlegroups.com>
Subject: intel-devsys A National Semiconductor Multibus I floppy controller

 

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[Jon Hales]

Roger

I didn't/don't envisage I'll be able to use the BLC8222. But that may be because I don't know enough about the extent to which it is compatible with Intel's protocols. I had assumed that National Semiconductor didn't emphasise compatibility with Intel's MDS systems - but that could be a mistake.

I would be grateful if you would enlighten me ('us', the group) about how this board could be integrated in an MDS-800 or a Series II.

Or, perhaps more straightforwardly, is the BLC8222 directly comparable to the Zendex ZX-200A - as demonstrated by Martyn?

Regards

Jon

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[roger arrick]

My understanding is that the BLC 8222 emulates the SBC201 AND SBC202 SD and M2FM controllers from Intel but this text from the databook doesn't confirm that like the Zendex 200 board data does.

If you want to sell that or trade it for something let me know.
I'd like to try it in my MDS800.

-Roger in TX

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From: intel-...@googlegroups.com <intel-...@googlegroups.com> on behalf of Jon Hales <jonh...@gmail.com>

Sent: Monday, September 4, 2023 8:57 AM
To: intel-...@googlegroups.com <intel-...@googlegroups.com>
Subject: Re: intel-devsys A National Semiconductor Multibus I floppy controller

 

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[roger arrick]

Here's the BLC-8221 from a 1979 data book
It's more bold showing SBC201 compatibility

-Roger in TX

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From: intel-...@googlegroups.com <intel-...@googlegroups.com> on behalf of roger arrick <ro...@arrick.com>
Sent: Monday, September 4, 2023 9:16 AM

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[Herbert Johnson]

On 9/4/2023 8:42 AM, Jon Hales wrote:
> Browsing Bill's intel_devel drive, I was reminded of Herb's useful
> Intel_FDC_field_guide.txt. The last line of Herb's file refers to
> "National Semiconductor BLC-8201 replaces SBC-201".

The document Jon mentions is

https://www.retrotechnology.com/herbs_stuff/intel_FDC_field_guide.txt

Which I created to list early Intel floppy controller boards, and
related products, primarily to track down MFM versus MMFM. It's
referenced in this document:

https://www.retrotechnology.com/herbs_stuff/m2fm.html

Both documents owe a lot to members of this intel-devsys group, from
discussions in 2018, prior to the forming of this google group.

The extent of "replaces", as I noted in the document, is derived from
two considerations. One is Roger Arrick's and Eric Smith's discussion.
The other is a general consideration that National Semiconductor made a
series of Multibus boards that worked alike Intel's early Multibus
boards. Essentially, National provided Intel-competing Multibus
board-level products.

How much alike? Read the manuals, look at the chips. My spider-sense
tells me "consider the FDC chip to consider compatibility".

> National Semiconductor also made a BLC8222 controller which supported FM
> and MFM and 8" and 5¼" drives. I came across one on eBay.co.uk

> <http://eBay.co.uk>. [describes documents]

>
> There may be further information in Nat Semi databooks of the early 1980s.
>

> I haven't learned about the OS used with Nat Semi systems of that
> period. Can anyone share what they know?

https://archive.org/details/NationalSemiconductor-MultibusBoardLevelComputerProductsDatabookOCR/page/n3/mode/1up

[caution: document is mis-described at archive.org]

In the table of contents, followed by my brief descriptions:

BLMX-80 Real Time Multitasking Executive [section 3 pg 3]
- ROM based with disk access
- mentions "Starplex disk format compatible" - National's development
system OS

BLC 8222 [section 6 pg 3], 8224 floppy controllers [6-6]

BLC 8222 - FM or MFM, 8" or 5.25" drives
BLC-8224 - same, supports 24-bit-address Multibus memory

Curiously little detailed descriptions of the boards. There were,
"hardware reference manuals" for them.

I don't recall more about Starplex. I can't find Starplex documentation
on the Web. That's all I have, from searching the Web. I did not read
Jon's scanned manual, Jon already has that information.

Regards Herb Johnson


--
Herb Johnson, New Jersey USA
http://www.retrotechnology.com or .net
preserve and restore 1970's personal computing
email: hjohnson @ retrotechnology dot com
or try later at herbjohnson @ comcast dot net

[Royce Taft]

I’ve seen some of these different user-compiled lists of cards for Multibus systems, and hoped to find a sort of system configuration guide to indicate which hardware is required for various goals but haven’t found anything yet.

Something similar exists for my HP 64000 series development system which lists exactly which interface cards and other hardware and software is required to emulate different systems. 

Does anyone know where a document for the MDS series II might exist?

Some information I’m hoping to find in such a document is what the purpose would be in adding an Intel SBC to an MDS series II system? Also required hardware and software required to emulate a microprocessor such as an 8080?

Royce

On Sep 4, 2023, at 09:25, Herbert Johnson <hjoh...@retrotechnology.com> wrote:

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[Herbert Johnson]

I'm sorry, but there's no singular document, about "the MDS SEries II".
There's a few MDS II manuals that collectively will give you an idea
about how MDS II systems worked, what Multibus cards they contained. But
to understand them, you'll need to read the software manuals about the
MDS development software, and the various hardware manuals on the cards.
Maybe you'll want to read descriptions of the Multibus 1; there was a
book or two about the Multibus.

Why read all that stuff, just to add some card? You say "I just added
cards to my HP64000 by following their manuals". Yeah. Those were cards
that had no other purpose, but to be put into that HP microprocessor
debugging system. So no need to review their engineering design or how
they interface to the 64000.

The Multibus is different. It's a general bus. Anything could work (by
itself) if it follows Multibus signaling. But to work with other
Multibus things? That's an engineering problem. There were *all kinds*
of Multibus computers designed and sold - to run factories, to run some
product, and as development systems. With all kinds of software.

The Intel MDS II is a expensive, scarce 1980's product, sold to 1980's
engineers, to do design and debugging work on Multibus boards and
systems and Intel processor systems. It was not a general purpose
system, it preceded such systems and a market for them.

No singular document. Do Web searching, There's Web pages about MDS
systems owned around the 21st century. They will link to sites with
Intel documents, and software. The MDS documents reference each other
and the boards in stock MDS II systems.

Why wasn't this simpler? When you got these in 1980, you got a stack of
manuals and a bunch of disks. YOu hired engineers and techs to use them.
There was no reason to write general books about the MDS systems; you
needed to be an engineer anyway. And this was all *new*! Everything was
unfamiliar. Now, those things are arcane, forgotten. It's new, again.

Just because fifty years has passed and today's computers are commodity
boxes and board that make themselves work - doesn't change how 1980's
computers worked, or change their documents, or their software. Finding
this stuff is mostly a private effort. The computers are left to
explaining themselves through their artifacts.

Regards Herb Johnson

On 9/4/2023 12:57 PM, Royce Taft wrote:
> I’ve seen some of these different user-compiled lists of cards for
> Multibus systems, and hoped to find a sort of system configuration guide
> to indicate which hardware is required for various goals but haven’t
> found anything yet.
>
> Something similar exists for my HP 64000 series development system which
> lists exactly which interface cards and other hardware and software is
> required to emulate different systems.
>

> Does anyone know where a document for the MDS series II might exist?
>
> Some information I’m hoping to find in such a document is what the
> purpose would be in adding an Intel SBC to an MDS series II system? Also
> required hardware and software required to emulate a microprocessor such
> as an 8080?
>
> Royce

[Eric Smith]

The BLC-8222 does emulate the Intel SBC-201/202 host interface, so there's a good chance of it working with ISIS II for 8", or for 3.5" HD configured to look like 8". 

ISIS II for the normal MDS systems doesn't know 5¼" geometries, but if you somehow constructed an ISIS II filesystem with the appropriate geometry on a 5¼" floppy, ISIS could probably access it, but not boot from it (unless you hacked up the ISIS.T0 code).

However, the BLC-8222 does not support Intel M2FM, so it will not read or write Intel MDS double density disks. It uses industry-standard MFM, commonly described as IBM System 34 format.

Controllers that do _any_ form of M2FM are uncommon, and there was no actual standard M2FM format, so Intel M2FM was not compatible with DEC M2FM etc. I've not heard of any disk controllers or chips that support Intel M2FM except the SBC 202 and some (but not all) Zendex controllers.

The Western Digital FD1781, TI TMS9929 and the Signetics 8X330 floppy controller chips can support some form of M2FM, and although they are somewhat configurable, it's not entirely clear that they can support Intel M2FM, and in amy case they are unobtanium and have a vastly different software interface than the SBC 202.

There's anecdotal evidence that a later Zendex product may have used the 8X330, but it is unclear whether that actually worked or was put into production.

Eric

[Jon Hales]

Eric

Thank you for your contribution to the discussion.

I suppose brand loyalty may have kept customers using the iSBC-202 with Series II and III.

Martyn's demonstrations (on YouTube) show that the Zendex ZX-200A - "with 3.5" configured to look like 8" " - copes with FM and M2FM - and can be persuaded to treat each side as a drive.

I had the impression that a 5¼ HD drive would also 'look like an 8" ', with an adapter to translate a 50-way cable to 34-way. It seems worthwhile to test this (not that there's any issue with the 3.5 approach). 

One candidate adapter is at: https://www.tindie.com/products/siliconinsider/8-floppy-disk-interface-50-pin-to-34-pin-adapter/

Another adapter is FD50TO34 by NF6X (on OshPark).

Regards

Jon

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[Eric Smith]

Hi Jon,

Martyn's demonstrations (on YouTube) show that the Zendex ZX-200A - "with 3.5" configured to look like 8" " - copes with FM and M2FM - and can be persuaded to treat each side as a drive.

Yes. I rrverse-engineered schematics and firmware of the ZX-200A before Richard recovered a manual that had the firmware listing. The actual "controller" consists of a huge amount of TTL logic and PROMs, rather than a VLSI controller. It's an evolution of another party's early controller design, which Zendex licensed because they were willing to adapt it to Intel M2FM.

If there were any way controllers that supported Intel M2FM other than the SBC-202 and some (but not all) Zendex controllers, it would be news to me.

I had the impression that a 5¼ HD drive would also 'look like an 8" ', with an adapter to translate a 50-way cable to 34-way.

The problem is that 8" and 3.5" HD use 300 RPM, while 5.25" HD normally uses 360 RPM, so the 5.25 normally can't fit 26 128-byte FM or 26 256-byte M2FM sectors on a track, whereas 8" and 3.5" can. This is the same reason a 5¼" HD on a PC is 1.2M (15 512-byte sectors), while a 3.5" HD is 1.44M (18 512-byte sectors).

Some 5.25" HD drives can be converted to 300 RPM, and that would work fine with ISIS II, but no longer PC-compatible.

Best regards,

Eric

[mark.p...@btinternet.com]

Eric

Rather than modify the drive, you could always increase the clock frequency, especially as the more modern media is likely to support this.

For 5.25”, you could use HD clock rate and use HD media if the drive supports this, but only write a partial track. Alternatively, modifications to the controller might be possible to achieve this, however it would require changes to the timing crystal and possibly the PLL components.

 

As to other boards, has anyone considered making a disk controller using a modern CPU. If you use and external data separator and PLL, a modern CPU would easily be able to handle the data decoding and encoding.

 

Note: ISIS II still uses 128 byte sectors for M2FM. It also uses 128 byte sectors for hard disks but the controllers could have synthesised this. Later versions e.g. PDS,  did support 256 byte sectors.

Mark

 

 

From: intel-...@googlegroups.com <intel-...@googlegroups.com> On Behalf Of Eric Smith
Sent: Saturday, September 9, 2023 11:49 PM
To: intel-devsys <intel-...@googlegroups.com>
Subject: Re: intel-devsys A National Semiconductor Multibus I floppy controller

 

Hi Jon,

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[Jon Hales]

Eric, Mark, Others

The attachments state that Shugart 80x and Teac FD-55G drives rotate at 360 rpm.

The feature of 'Mode 3 / Japanese Mode' that allows some 3.5 inch drives to replace 8 inch drives is that this mode rotates the disk at 360rpm. [3.5 drives are not all capable of this].

Or [...] have I missed some detail [...]?

I'm sure some of us would be interested to see the firmware of the ZX-200A.

Mark: 

As you say, Intel M2FM has a track capacity 6,656 bytes; 77 tracks equals 500 Kb (4004 sectors at 128 bytes). That appears less than the 5¼ HD 600 Kb per side (which requires space on the track for data to identify the sectors, CRCs, etc.). The 15 x 512 byte sectors store 7680 bytes.

By 'modern CPU', I assume you mean one some fraction of the die size of the 8080. Perhaps a Pi Pico.

Regards

Jon

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[Eric Smith]

On Sun, Sep 10, 2023, 05:17 Jon Hales <jonh...@gmail.com> wrote:

The attachments state that Shugart 80x and Teac FD-55G drives rotate at 360 rpm.

My apologies, I had the RPMs wrong and will have to think more about why 5.25" HD (PC 1.2M) doesn't pack as much on a track as 3.5" HD (PC 1.44M).

I'm sure some of us would be interested to see the firmware of the ZX-200A.

There's a listing in the manual. My reverse,-engineered source, from before the manual was recovered, is on GitHub:

https://github.com/brouhaha/zx200a-fw/

[Herbert Johnson]

On 9/10/2023 6:27 PM, Eric Smith wrote:

> My apologies, I had the RPMs wrong and will have to think more about why
> 5.25" HD (PC 1.2M) doesn't pack as much on a track as 3.5" HD (PC 1.44M).

I cover much about basic disk formats and speeds and densities here:

https://www.retrotechnology.com/herbs_stuff/drive.html

These things, and how to adapt 3.5 and 5.25 inch drives, come up with
every new new model of some floppy disk emulator or floppy disk
flux-read/write device. A review of recent or past (hobby) products will
find the same discussions. Before that: discussions of the various
floppy controllers made in their eras, all the way back.

My page sticks to the basics: drives, media, more or less common formats
in the 20th century. No controllers, except unique ones (M2FM is unique).

Still, new things come up. I did not know about high-density 8" disks
and drives until a few years ago. Yes, different media, different
drives, different heads than common 8" drives. Who knew?

One disk format is different from another format, so they won't produce
the same results. It's not "why" but "how", details are documented
somewhere, I cover the highlights. The capacities are happenstance.

Regards Herb Johnson