Pdp 8 emulator mac os x

Sunday will feature [Bob Frankston], co-developer of VisiCalc. There will be very important people here all weekend. We will, of course, be posting a lot of stuff from the event. This would be fairly cheap to build, and has the added bonus of not weighing several hundred pounds. Instead, [Oscar] is putting everything on USB sticks. Oh, if anyone knows how to connect a Pi to a VT technically a , leave a note in the comments. Card punches and even readers are becoming rare and expensive.

Undaunted, [Antiquekid3] threw some modern hardware into the mix, and used an Arduino Uno as a Documation to Serial interface. It also had a serial interface which made outputting data a snap. Plotting the data with a spreadsheet results in a nice linear set of data points. Of course, no one knows what the data is supposed to mean! Want more punch card goodness? By using our website and services, you expressly agree to the placement of our performance, functionality and advertising cookies.

Since the last report all of our efforts have been on the A sub-project, to get this to a natural break-point; so that we can concentrate on polishing the S emulator ready for release. We are still missing the second paper tape for E1DS the overlays , but have recreated more of the missing overlays, so that we can now use magnetic tape in addition to basic peripherals cards, paper tape and printer.

We have started looking at discs, but the UDAS implementation, with the little information we have, is proving difficult. Again, the same plea as the last time — Has anybody any information, listings etc. One Saturday in December the machine crashed whilst running George 3 and could not be restarted. The symptoms were a hang during CME microcode loading, but not always at the same point. Normally when faults occur the first recourse is the CUTS diagnostic test programs, but in this case all tests passed except for the store test MHR7 which has been failing for some years due to a Hamming logic fault on one of the sub-store control boards.

Following some more diagnostic work it became clear the crashes were due to a timed out SCU transaction to the store. The spare sub-store control board was fitted to allow the full store test to be run, but it so happened that this also fixed the issue!

PiDP-8/I Software: PiDP-8/I Changes

Evidently this board has developed a second fault. Unfortunately we now have no spares, so the task of constructing a test jig for diagnosing faults on the more complex boards has got a bit more urgent. The existing test jig only drives half the board pins, which was sufficient for a lot of the DCU boards but not for the SCU.

Meanwhile the intermittent OCP Before Christmas we narrowed down possible causes as a bogus under-voltage comparator trip, a control board logic fault, or a bogus signal from one of the opto-isolators involved in over-voltage detection.

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The former two were then ruled out by board swapping, leaving only what was considered to be the most unlikely cause! An actual over-voltage signal from one of the power supplies was thought to be impossible because it latches in the supply and thus the over-voltage LED would remain lit after the OCP control circuits shut off all the supplies. To resolve the issue once and for all the four channel scope was wheeled out and connected to the After an hour the supplies tripped off and the scope triggered, showing a large spike on the over-voltage line.

It was clear from the other traces that no over-voltage had actually occurred. Three scope channels were then moved to the other side of the opto-isolators for each of the three parallel After another hour or so the scope triggered again and this time showed a clear spike on the over-voltage line coming from one of the supplies.

So it appears that either the signal is actually coming from the supply, there is a wiring fault somewhere, or there is an intermittent internal short in the opto-isolator in question. The suspect supply was swapped with the spare after suitable running in of the spare on the bench to return the machine to operation, and then attention was turned to testing the suspect supply on the bench.

comp.emulators.misc Frequently Asked Questions (FAQ) [1/3]

As reported some time ago the Bombe Rebuild website was lost to readers when the organisation that was hosting it withdrew its facilities at short notice. The original has now been updated and incorporated into a new site with much wider coverage: not just as before the ten year or so rebuild phase. The plan is that the site will be expanded over time with new Bombe related subjects added so viewers might see place holders appear from time to time or only partial subjects be covered as a topic is developed.

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Hopefully, these will be short-lived. Following the Meccano D. Any more?

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After years, Belgium has finally got around to abolishing its telegram system. Latterly used by a tiny number of organisations, largely for legal reasons, it was switched off in December. But a surprising number of national telegram systems remain in use including in New Zealand which abolished its service in only to reinstate it four years later.

Whether the telegrams are still delivered by a callow youth on a low-powered motor cycle is not known. This story is thought to be a fiction invented by Mr Grant. She led a successful pioneering campaign for equal pay when it was discovered that Ferranti paid women less than men for the same work. On page 29 Ann Moffatt writes concerning the early days of computing exhibits at the Science Museum in London.

It seems unlikely that power has been applied from that day to this. What a glorious achievement it would be if Exciting news from Bletchley Park! We are delighted with this solution and welcome the opportunity to remain part of the overall visitor attraction at Bletchley Park. We thank the Bletchley Park Trust for their co-operation over the years and are pleased that the story of the Bombe will remain very much part of the story that it tells.

As a pre-computing electro-mechanical device, the Bombe will help our visitors better understand the beginnings of computing and the general thought processes that led to the development of Colossus and subsequent computers. The story of the design of the Bombe by Alan Turing, the father of computer science, leads very appropriately into the eight decades of computing that we curate. The Bombe will be housed near Colossus in a new gallery.

A crowdfunding campaign can be found via the TNMoC website www.


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The Society has its own website, which is located at www. It contains news items, details of forthcoming events, and also electronic copies of all past issues of Resurrection , in both HTML and PDF formats, which can be downloaded for printing. At www.

Tom has been Chair for an outstanding 18 years taking over the job from the late Prof. Frank Sumner in Quite how he found time to support the CCS is something of a mystery. Gordon assumed the position of secretary in following a career in ICL during which he built up the Design Automation Division providing the tools needed to support the design and manufacture of several generations of Mainframes.

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The Society owes these two gentlemen a huge debt. Not just for keeping the show on the road, but for managing and developing a vibrant and active group over a long period. Happily, volunteers have been found to fill the vacant posts. We welcome Bob Geatrell and Alan Pickwick as the new Chair and Secretary who, by the time this edition of Resurrection is published, will be taking up the reins.

In Mr Tony Gough presented me with a box of Elliott documentation dating back to the time he had been employed by Elliotts at Borehamwood. The manual describes a version of the language for the NCR-Elliott , succeeding earlier versions for the M , and a M to B cross compiler Program commands similar to COBOL are written in a stylised English form intended to make programs readable by non-programmers.

A significant difference is that Language H does not have a direct equivalent of the COBOL Data Division to describe the structure of input data, output data and working storage, but instead derives this information from how data is used in program commands. The author leaves it to readers to make their own judgement as to how successful the language H designers were in meeting these goals. He can be contacted at andrew herbertfamily.

Part 2 of this article will appear in the next edition of Resurrection. Contemporaneously, a devoted fan-base for the machine began, which continues today with new machines being built and development of software for the computer continuing. The PDP-8 in was a transistorised desktop computer albeit a sturdy desk was required with 4k of bit word core memory, an easily understandable order code, extensive documentation and practical system software. Often paired with an ASR33 teletype, the machine was personal in the sense it was affordable by a small team and operated by one person at a time but was also very self-contained.

Each flip-chip had a specific function and typical examples included a flip-flop 12 of which could be linked to form a register , inverters and standard logic gates. To satisfy their initial investors Digital did not ostensibly sell computers in their early days but sold components such as flip-chips instead. Indeed, PDP stands for Parallel Data Processor — carefully avoiding the term computer as those early investors thought few would be willing to buy a computer from this small start-up company.

The new machines were mostly compatible with the previous generations and system software was often transferrable. However DEC regarded the machines as platforms for their new office software and discouraged their use as a general PDP The DecMate series was manufactured until In all, the PDP-8 was reimplemented with new technology ten times over a period of 15 years. In , Bob Supnik, formerly an engineer at DEC, produced a general multi-system and multi-platform emulator called SIMH, which was based on his previous work dating back to the s.

SIMH is a text based programme that lets the user define the machine they wish to emulate and build virtual devices and media packs. While real peripherals such as disc drives and tape drives were generally more affordable from DEC than those from the traditional mainframe suppliers, users were of course limited by space, funds and available power. There is no such limitation with virtual devices and it is easy to add dozens of RK05 disc drives to a virtual PDP This occasionally brings out some shortcomings in the system generation scripts where the original programmer assumed no one would ever have more than eight disc drives!

As SIMH is designed to emulate many different systems, it does not attempt to simulate the target system from the logic level upwards, but rather emulating instruction by instruction. Once the basic structures of the processor have been defined, the action of each instruction type can be handled individually. Having used SIMH to build an emulator for a quite different processor it is possible to generate a HALT whenever a new unhandled instruction is found, and then keep adding code for each new instruction until the machine finally runs.

Bernhard Baehr has produced a GUI emulator that is shown below. As well as an interactive front panel, this emulator allows the internal processor state to be continually monitored. It supports visual hard disc drives and DecTapes that spin! The virtual teletype even makes the quickly annoying noise that an original ASR makes! The FPGA chip is an array of programmable logic blocks which can be programmed as simple logic gates and flip-flops through to registers and memory arrays. The open-cores project includes a complete HDL Hardware Description Language definition of the PDP-8, which is typically downloaded to a development system that includes sufficient switches and lights to represent the PDP control panel.

The single chip PDP-8 the series of Harris microprocessors used in the DecMate machines is still available from various second-hand sources, which led Bob Armstrong of SpareTimeGizmos to develop the SBC — a new single board system using the original microprocessor but with new circuitry to support modern hard discs.

The difficulty of obtaining original CMOS-8 microprocessors sadly limits the use of this machine. Additional code on the Pi reads those values and updates the front panel display. Given a sufficiently powerful variant of the Pi, the emulation also modulates the brightness of the LEDs to mimic the behaviour of the original incandescent lamps! It is this new realisation of the PDP-8 that has generated the most interest in those new to the machine, partly because of the ease of building the kit and partly because of the very attractive design.


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The question that remains is why is there all this activity and enthusiasm for a computer designed more than 50 years ago? Yes, nostalgia for a machine many of us used in our early days in computing, but why the new generation of enthusiasts for a machine that came out of production after many of them were born? The PDP-8 is very well documented; DEC produced detailed descriptions of exactly how the machines worked and of course all the circuit diagrams, and both DEC and DECUS provided a wealth of program examples and useful routines as well as the source-code for all the utilities.

All this information is now readily available on the web and includes scans of all the original DEC handbooks. Designing new emulators and hardware replicas is therefore made much easier with this information available. Development of at least one operating system for the PDP-8 continues today and some of those new to the PDP-8 are already submitting changes and fixes. Many of these new PDP-8 programmers have full-time jobs in IT, but are typically constrained by modern development frameworks and the continual need to learn new techniques and programming paradigms.

The simpler world of the PDP-8 is an attractive alternative during their down-time. It does highlight the disconnect between users of modern off-the-shelf solutions and the research and technology that went into building them. If you wish to toggle in a simple light chaser to the front panel then here are some switch commands which can be used:. If you plan to run the emulator repeatedly or for a project, consider downloading the emulator to your own machine or server. This will significantly speed any of the emulator disk accesses and response times.

Some of the really interesting ones can be found by googling terms such as "vhdl pdp 11". A different approach to Javascript PDP 11 emulation can be found at www. There is more PDP 11 history at www.