This part of this MPS10 document goes over each of the modules making up the MPS10 system

http://www.willegal.net/blog/wp-content/uploads/2019/11/MPS-modules.pdf

Although this 8008 system has a feature set that is similar to other 8008 computers, there are some differences that make this system unusual.

Memory support for the MPS10 is typical of other 8008 systems, with from 1k to 16K of memory. The SRAM module used 2102 type memories and the EPROM card took up to 16 1702A EPROM chips.

One of the unusual features is the UART incorporated into the main CPU card. The UART supports a full duplex serial interface.

The main processor board also has a berg connector intended to interconnect with the Monitor/Control module with a “standard cable”. The Monitor/Control Module is mounted in it’s own cabinet, outside the M-series chassis that holds the rest of this system. The monitor and control module was intended for maintenance and program debug only. It supports typical debug operations such as read and write memory, running, stopping and stepping programs. It also contains a ROM with bootstrap program.

Finally, the MPS10 included an External Event Detection Module (EEDM) which supported up to 8 external interrupts and a power fail detection circuit. I’d say the extra external interrupt support was added because of the vision of using this system in process control applications and the weakness of the 8008 regarding interrupt handling capability.

Also mentioned is the foundation module, which is supposed to support user hardware interfacing. I don’t know much about the DEC “M” series chassis, but it appears that these foundation modules are some sort of standard prototyping boards, that were already being sold by DEC.

This short section of the MPS10 document first asks when one should choose a microprocessor over hardwired logic.

http://www.willegal.net/blog/wp-content/uploads/2019/11/MPS10-why-perf-PDP.pdf

There is a paragraph discussing how to evaluate micro-processors, which is basically the same as evaluating any computer. The next section asks why use the Intel chip – the answer being that it’s about the only one available. Perhaps at the time that it was written, the IMP-16 wasn’t known about or available or the IMP-16 was dismissed for other reasons.

The next section starts discussing the MPS10. One thing that is called out, is that the MPS10 is a member of DECs M series module line. I don’t know anything about the M series modules, but perhaps some existing M series modules would be able to interoperate with the MPS10.

The next section lists the five modules that make up the MPS processor system. These modules are:

The M7341 processor module

The M7342 monitor/control module

Three size variations of the M7344 Memory module (1K, 2K, 4K)

The M7345 4K Prom memory module

The m7346 external event detection module

The last part of this section discusses the relationship of the MPS10 with other Digital Equipment Corporation Computers. The first statement of this section states that the MPS10 is not a minicomputer and is not intended to compete with minicomputers. It was designed to be a dedicated controller, a replacement for fixed logic designs.

“It should be considered to be an extremely useful augmentation of and addition to, DEC’s existing arsenal of processing devices.”

One thing to keep in mind, is that DEC had a very successful line of minicomputers, and undercutting that business from within the company, would have been a very risky proposition. Any change of architecture away from the PDP series would leave a potential customer, the option of evaluating systems from competing businesses as well as any new DEC architecture. The developers of the MPS10 had to be careful to not threaten the existing DEC business, which could account for some of the language in this document.

So far, I’ve tested power rails and they appear to be reasonably good. The SCELBI power supplies provide +5 and -9. In addition, components on this card need -5 and +12. The -5 is generated on board using a series of voltage dropping diodes connected to the -9 supply. The +12 is generated with the little converter that can be seen mounted on top of the board. That converter has been documented in a few previous posts. The -5 supply sits at something like 5.6, which is a bit on the high side, but I’ll just go with it. The +12 looks pretty good, as it is sitting at 11.8. Voltages could change a little bit in actual operation as the testing was done without a running clock. I’ll definitely keep an eye on that as I move forward with more testing.

I am expecting the crystal that I need to arrive next week. The installed crystal is something I had on hand in a parts bin. It is something like 3.6 Mhz, which I figured is close enough that I could use it to check clock generation and general performance of the timing portions of the circuit.

The next section of this MPS10 document contains information about recommended applications.

http://www.willegal.net/blog/wp-content/uploads/2019/10/MPS-10-applications.pdf

The main thing to take away from this section is the first point. The end user is envisioned as a “OEM or large end user (corporate OEM)“. Though, it is also envisioned as going into “extremely price-sensitive” applications, the MPS10 was not envisioned as a home or hobbyist machine or even applicable to small businesses.

I think that this is typical of many currently mis-understood early micro-processor based systems. The companies manufacturing these systems didn’t really want to be bothered by small one-off end users, who might end up requiring a very large amount of support for very few or even single sales. The vendors of many systems like the MPS10 were looking for volume sales opportunities, because they knew that tools and support infrastructure was very limited in scope. In this case, DEC was looking for sales to tech savvy companies that could work through most of the technical issues on their own. This is clearly called out in the statement: “Is hardware-design-oriented and has in-house technical capability”.

A similar comment can be found on page 66 of the Micral user’s manual.

Most companies selling these early, very primitive, microprocessor based computers were looking for tech savvy companies to buy the computers and embed them in end-user applications.

The next section of the document list possible applications that this system may be used for. These days, every one of these suggested applications would be classified as a embedded systems application. The last part of this section list a couple specific embedded applications. The first one, a process control application, includes a flow chart that fits on one page. This should give the reader a good idea of what kind of application was deemed suitable for the MPS10 microcomputer. There is absolutely no mention of hobby or learning type applications in this document.

The first small SCELBI ad contained a vastly different message, “DESIGNED FOR THE ELECTRONIC/COMPUTER HOBBYIST!”. What really made the SCELBI, MARK-8 and similar systems so different than regular computers of the time was the marketing.

This series of posts will be a detailed review and commentary about the MPS10 Microprocessor Set manual that I recently acquired. First I’ll provide a bit of background.

I first encountered information about the Digital MPS-10 8008 based computer system several years ago. There is a lot of information about this system in the bitsavers archive at: http://www.bitsavers.org/pdf/dec/mps/. In fact, there is nearly enough information online, to enable someone to build a reproduction of the hardware. However software information is very sparse.

When I won the recent eBay auction for a DEC MPS10 manual, I wasn’t sure what I had won. In fact, I had forgotten about the bitsavers information that I had already downloaded and examined. After reviewing this manual and comparing to the information downloaded from the bitsavers website, I’m pretty well convinced that this manual was a DEC internal product plan of some sort. What makes this manual interesting, is the perspective it gives the modern reader, regarding marketing potential of the microprocessor based systems that were just coming into existence and their potential impact on the mini-computer business. As a mini-computer industry veteran, I figure I can provide a unique analysis of this document.

I plan on reviewing this document section by section and I’ll start with the first 5 pages, which is an overview of just what a microprocessor was.

http://www.willegal.net/blog/wp-content/uploads/2019/10/introduction-logic-products-MPS-10-plan-1.pdf

To start with, the introduction in this “book” describes the microprocessor and the system made up with a microprocessor. It notes that the complete microprocessor system ends up being made up of from 25 to 40 ICs, quite a few more than in theory. It also notes that future systems will benefit from N-channel MOS and bipolar TTL, which will contribute greatly to increased speeds in future devices.

The next paragraph describes the advantages of microcomputers. This section compares microprocessors primarily to special-purpose logic, rather than mini-computers. The listed advantages over special purpose logic include faster product design time, changes easier to implement and an increase of reliability.

The next section compares the microcomputer to the minicomputer. Differences are described in a chart and include the optional use of core memory in the minicomputer. Software on the minicomputer is described as being more complete and comprehensive compared to more basic tools for the microprocessor. In addition, programs must be created off-line on a more capable host machine, such as a PDP-8 in the case of the microprocessor. Price is listed as medium on the minicomputer versus low on the microcomputer. The last comparison is support and service, where the microcomputer is listed as having no field service compared to the full field service available to the minicomputer owner/operator.

While this information seems rather basic and obvious to the modern reader, remember that microprocessors were brand new devices at the time, and the authors believed that they needed to cover the basics of the microprocessor. Also keep in mind that the authors worked for DEC, which generated a vast majority of it’s current revenue directly or indirectly from the PDP series of mini-computers. Though the authors were obviously excited about the possibilities of the microprocessor, they apparently needed to make sure that the reader understood that the microcomputer was supposed to be a replacement for special logic designs, not a replacement for DECs successful line of mini-computers.

I recently obtained this MPS10 book from eBay. The Digital MPS10 was a little known Intel 8008 based system produced by Digital Electronics Corporation back in 1974. I ran across a reference to this system a few years ago.

Since then I have had a standing search on eBay for MPS10 items. This is the first relevant item that actually showed up. I managed to win the auction at a quite affordable price. The book is kind of interesting as it appears to be almost more of a corporate marketing plan than an end user document, though it could be the later. I plan to scan it and share the contents on my website or blog.

I’m guessing that the Logic Products group at Digital produced logic cards for the rest of the business, not complete computers. Perhaps someone with more knowledge of DEC’s internal organization could add a comment with more accurate information about what the Logic Products team were responsible for.

I’ve had the layout done for a while, but haven’t had time to build them. Thinking I might as well get the PCBs made, I finally pulled the trigger.

As far as building and testing them goes, free time is still scarce, and I will not get the needed 5MHz crystal until early December, but I have the rest of the parts on hand or arriving shortly. I may be able to build them and run them with an external frequency source, so the lack of a crystal may not be a complete show-stopper. It may or may not be quite a while before I get them up and running.

One other thing. I explored getting these boards made in China, but since I had a batch made, the end cost was about the same as using Advanced Circuits. Getting one or two made would be vastly cheaper if I had them done in China, but I always have taken the chance and have reasonable sized batches made.

Original Digital Group Video Cards are scarce, but I don’t believe that the market for these cards will be very big. I expect the 20 that I had made, will cover the demand, plus some.

I finished the reproduction Digital Group Video Card PCB layout a few months ago. This summer, I’ve been busy with other projects, but I’ve finally ordered a batch of PCBs. I should have them in hand in another week or so. I have all components in hand or on order. I’ve found the 5 MhZ crystal is not exactly common. I currently have a few on backorder at Mouser. Expected ship date is early December, so I may not be able to fully check out this card for a while.

I don’t expect the software to be very difficult, as the hardware interface is very basic. If you want to change any characters or do anything like scrolling, it looks like you need to write out the whole page of display data. The easiest thing might be to keep a mirror of video memory in main memory and write out the whole thing anytime that there is a change.

Here is my test setup for the finished DC-DC converter. The power supply supplies 5 volts DC. The bread board includes filter capacitors and a potentiometer that is used to supply a load. These items emulate the final circuit when the DC-DC converter is installed on the Digital Group video card.

The supply shows that the current draw is 38 milliamps. With the potentiometer set at about 1K ohms resistance, the DC-DC converter is supplying 11.44 volts, which I think will be sufficient for the final application on the Digital Group video card.

One final comment on this converter. This thing seems very small to me. In fact, when I first made the PCB, I wondered if I had mistakenly scaled it to a smaller than 1:1 size.

Here is the finished board, ready and waiting for a Digital Group video card.

The design for this converter is documented in previous post. This is a homemade PCB that will mounted onto the Digital Group Video board.

Not my best work, but it will do.