test-drb

test-drb@ccmp.vtda.org

101090 discussions

by cc＠informatik.uni-stuttgart.de

Hi, do hardware manuals for the TWIN exist? And does any other TWIN system exist? It seems it is a completely forgotten and lost development system. Christian

8 years, 2 months

Ideas for a simple, but somewhat extendable computer bus

by jnc＠mercury.lcs.mit.edu

> From: Charles Anthony > a hybrid PDP-11 (16 bits) / PDP-15 (18 bits) on a shared bus (UNIBUS?) That's a UNICHANNEL-15: it allowed devices on the -11 to do DMA directly into the PDP-15's memory through the MX15-B Memory Multiplexer. Odd factoid: this UNIBUS could run in 18-bit mode (!!), where the UNIBUS' two parity lines were recycled into 2 extra data lines. Some DMA interfaces (e.g. the RK11) could support this; in this particular case, it allowed the PDP-15 to use RK05 drives. Noel

8 years, 2 months

Idle question: Color of tape coatings

by cclist＠sydex.com

While working on some old (again!) half-inch tapes, I note that some of the very old ones have an oxide coating about the color of milk chocolate. Newer ones are anywhere from dark chocolate to black. Reel construction is another aspect. The really old ones tend to be all clear plastic, including the hub area. Newer ones have either a black plastic reinforcement to the hub or employ an aluminum sleeve. In most cases, the oldest of these is from around 1964, but probably older than that, as the only clues I have are dates placed by the tape librarian when a tape is put back into the pool or a label indicating when the tape was last recertified. Was there a date after which *all* half-inch tape became the dark brown to nearly black in color? --Chuck

8 years, 2 months

Sync on Green RGB video

by dj.taylor4＠comcast.net

I have a couple of vaxes that output 'unique' video, Alpha 3000 300, Alpha 3000 400, Vax 4000 VLC, and Vax Station 3100 M76. The Alpha and VLC each have a 3W3 type of connector and the 3100 has a 15 pin DEC designed connector. What does it take to connect these to inexpensive, modern VGA light weight monitors? Doug

8 years, 2 months

Ideas for a simple, but somewhat extendable computer bus

by spacewar＠gmail.com

On Nov 20, 2017 7:41 AM, "Tapley, Mark via cctalk" <cctalk at classiccmp.org> wrote: Catching up late, sorry if this is an old question, but what did the Digital Group computers use? My recollection is that they offered cards with 6800, 6502, 8080, and Z-80 CPUs on the same bus, and that part of the system seemed to work reasonably well. The Digital Group had two separate buses, a memory bys and an I/O bus, as well as two other slot types incompatible with either bus, for a CPU card and a TVC (video and cassette) card. They didn't support interrupts or DMA on any bus. If you wanted to use an interrupt, you had to wire it over the top. Doc Suding said that he didn't put interrupts on the bus because (paraphrasing) they are complicated and you don't need them. As you say, they did support various CPUs, but not more than one in a system. I wouldn't recommend that anyone consider The Digital Group as an example of good bus design.

8 years, 2 months

Looking for Silent 700 model 787 manual

by chrise＠pobox.com

I recently acquired a TI Silent 700 model 787 terminal. This cc 1980 unit is an interesting member of the Silent 700 family as it is capable of 120 chars/sec printing and has an internal 300/1200 baud direct connect modem that does Bell 103, Bell 212A and Vadic modulation in both originate and answer modes. It's a got a DB25 on the back for directly connecting serial but I don't have any documentation on how to choose the internal modem vs the DB25 for comms or any pinouts for this DB25 outside the usual expectations of RS232 on a DB25. Seeking any documentation that might be around. Happy to cover copying costs or purchase a manual if it is excess to someone's needs. Chris -- Chris Elmquist

8 years, 2 months

Ideas for a simple, but somewhat extendable computer bus

by jnc＠mercury.lcs.mit.edu

> From: Allison >> I would seriously consider shared data/address lines, like on the QBUS. > QBUS is wrapped around a subset of PDP11 and the unique processors made > to fit it. I did say "like ... the QBUS", not "the QBUS"! I was just trying to make the point that the original sketch assumed separate address and data lines, and that's an assumption worth looking at. > The bottom line is for every bus you have to get on and off with > devices to buffer ... The more you use the less card there is for other > things Yes, but that cuts both ways: multiplexed address and data also saves you a lot of bus transceivers. Noel

8 years, 2 months

Ideas for a simple, but somewhat extendable computer bus

by brain＠jbrain.com

I'm currently working on a single board computer system, designing from scratch partially as an education experience, and also as something that might be of interest to others. I've laid out the first version of the SBC, and I realize it would cost nothing to add an edge connector on the PCB, allowing expansion options.? As well, assuming the design has any merit, I can see creating one of these SBcs for each family (8080/Z80, 65XX, 68XX, and maybe even 16 bit options like TMS9900, 68K, etc.) However, as the design is not *for* any purpose, and I've never designed a bus that could be shared among multiple CPUs, I am wondering what bus layout would satisfy the following criteria: * At least enough to support a traditional 8 bit CPU (A0-15,D0-7, RESET, READ/WRITE,CLOCK,INTERRUPTS) with potentially a few more address bits (A16-23) * Minimal number of bus signals to support multi-processors and peripheral cards, but not so few that usefulness is severely crippled * Easy to implement (minimize need for logic that serves to solely handle the bus) * (If 16 bit data bus is part of the design): Easy for 8 and 16 bit CPUs and peripherals to share the bus (Maybe this means 16 bit units need to be constrained to 8 bit, not sure) * Works out to a size that I can buy edge connectors cheaply (62 pin .100" connectors are looking like my cheap option at present) I looked at home computer busses (Atari, Apple, Commodore, Tandy, TI) for a bit of inspiration, but they all seem overly simplistic (not horrible, but hate to just punt on the idea).? I also looked at the ISA bus and the S-100 bus, but they are a bit overwhelming to me (I can grok all the signals, but ensuring they are all responsive seems like it will drive more logic be on the PCB jsut to handle the bus, and I am trying to keep costs very minimal). Thus, Is there a bus (or a fraction of a bus standard) that I should consider to accommodate the above?? Anyone else interested in this idea and in a collaborative mood? Jim -- Jim Brain brain at jbrain.com www.jbrain.com

8 years, 2 months

Wanted: HP7970 hub mech

by cclist＠sydex.com

This is a pretty far-fetched request, but here goes. The quick-release levers on the HP 7970 tape drive are plastic. They're starting to get brittle. I've got one that's showing cracks, so I swapped it the the one on the takeup reel, as that one doesn't see as much action as the one on the supply reel. What I'd really like to find is the older twist-to-tighten mechanisms on the 7970. I suppose I can get busy in my shop and make some, but I'm wondering if there are any lurking in someone's hell box. Thanks for reading! Chuck

8 years, 2 months

Ideas for a simple, but somewhat extendable computer bus

by jnc＠mercury.lcs.mit.edu

> From: Allison > simple 16 data, 24 address likely 6 lines for basic control plus others > your up to 50+ lines I would seriously consider shared data/address lines, like on the QBUS. It doesn't add _that_ much complexity to share the lines (I did a slave device using only 74xxx parts, and it was dead simple - probably a goal of the designers), and it will really drop the pin count. The speed impact is not too bad - on reads, where the address and data naturally happen at different times, it can be none. Noel

8 years, 2 months

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