test-drb February 2021

test-drb@ccmp.vtda.org

113 participants
93 discussions

by aek＠bitsavers.org

I'm assuming these are 960s Not very often you see paper tape software for them Price is absurd for the mixed bag that is there https://www.ebay.com/itm/Texas-Instruments-Mainframe-Computers-With-Parts-a…

3 years, 2 months

PDP-11/70 progress (and a cry for help)

by derschjo＠gmail.com

Hi all -- Thought you all might be interested in an update, and I'm also looking for advice in debugging the current issue I'm hitting. After replacing the clock crystal on the TIG, the system started showing signs of life, but the Load Address switch would stop working after being powered on for 10-30 seconds, but would work fine single-stepping via the KM11. Brought the DAP board out onto the extender for debugging and the problem went away. Reinstalled the board after cleaning the slot (again) and the problem hasn't recurred since. First bad backplane connection, I'm sure it won't be the last. After this, addresses could be loaded, data could be toggled into memory. But instructions wouldn't execute; Tracing through the microcode with the KM11 indicated that the microcode flow was aborting early and returning to the main console loop (via BRK.90) before the instruction fetch at FET.00; this was due to the TMCB BRQ TRUE H signal being stuck high. Probing of the TMC board revealed a bad 74H30 at E70, which had its output stuck at 1.65V or so, just high enough to confuse things. Now instructions would execute but the PC would contain garbage after execution of an instruction, after tracing the microcode and staring at the flow diagrams all signs pointed to the PCB register (twin to the PCA register that is used for storing PC data) having trouble. Garbage in the PC after execution was always in bits 6-11, everything else was fine, which pointed to a 74S174 at H47 on the DAP board. Replaced and now instructions execute! Mostly. They seem to execute properly when single-stepping instructions, or running off the RC clock at a clock rate of about 16-20Mhz, any faster than that and things stop working correctly. This is what I'm currently banging my head against -- if anyone has any experience with the 11/70 or wants to stare at the manuals for a bit (and who doesn't?), I'd appreciate any extra input. There are a number of different issues, I'm currently focusing on two-operand instructions that take an immediate argument (MOV #10, R0, or ADD #42, R5) for example. The behavior here is a bit befuddling and I can't quite figure out how it ends up happening, given the microcode. I'll use ADD as a representative example. An ADD #10, R0 instruction (followed by HALT) poked in at address 1000 executes properly -- R0 gets 10 -- but afterwards the PC is corrupted: it contains 2, rather than 1004. In the general case, "ADD #X, R0" ends with PC containing 2 + <original value of R0>. (MOV shows the exact same behavior, except that there's no addition, obviously.) This value of PC is shown in the Address lights, as well as when examining the register from the front panel (at 17777707). When single-instruction-stepping the processor this instruction executes perfectly: R0 gets R0+10, PC is 1004 afterwards (both in the Address lights and when examining from the front panel). I have verified with my logic analyzer that when running normally (i.e. not single-stepping) the microcode executes the proper sequence of instructions -- which is the same as executed when single-stepping except at the very end: In FLOWS 4, after the D00.90 instruction executes, a branch is taken to BRK.90, which exits back to the console loop. I don't believe there should be any other differences in execution between the two paths -- other than the branch at the end there are no conditional branches or conditional operations based on whether the CPU is single-stepping or not. There's a signal somewhere in there that has just gone a little bit slow... the trick is finding it. For reference, the microcode sequence (starting at FET.03, see pg. 5 of http://bitsavers.org/pdf/dec/pdp11/1170/MP0KB11-C0_1170engDrw_Nov75.pdf) is: 334 (FET.03) 260 (FET.10) 343 (IRD.00) 022 (S13.01) 027 (S13.10) 205 (D00.90) 260 (FET.10) 343 (IRD.00) 010 (HLT.00) 316 (HLT.10) 164 (FET.04) 240 (BRK.90) 352 (BRK.00) 170 (CON.00) You can see it fetching and executing the ADD instruction, then returning back to FET.10 and executing the next instruction, which is a HALT instruction (because all other memory contains 0 at this point). I believe this is what causes the "+2" portion of the final (incorrect) PC value. (What's extra odd -- literally -- here is that if you start with a "1" in R0, the final PC is 3... seemingly indicating a fetch/execution of an instruction at an odd address, which you'd think would cause a trap instead...) I've been staring at this awhile and I'm puzzled; everything seems to execute properly, the instruction is fetched and decoded, and the immediate value is fetched, the ALU does the right thing and the result is properly stored in R0. And then the PC gets screwed up, and I'm not quite sure how that's possible from looking at the microcode, so I'm not quite sure where to start looking. I sort of suspect the PCB register again, as this is related to the difference in behavior between single-stepping and normal execution: the branch back to the console loop *doesn't* update PCA from PCB, whereas the branch back to the fetch / decode loop does. Anyone have any bright ideas as far as what to poke at? Thanks as always, - Josh

3 years, 2 months

Systems Concepts SC-4 computer

by jnc＠mercury.lcs.mit.edu

> From: Lars Brinkhoff > Anyone ever heard of the Systems Concepts SC-4 computer? Given the SF address, and Peter Samson's signature, this is the _the_ Systems Concepts. Never heard of the SC-4, though. One oddity: the cover letter is dated 1972, but it talks of "the main G.E. computer". GE's computer business was sold to Honeywell in 1970, though? Noel

3 years, 2 months

IndiZone collections

by compoobah＠gmail.com

Curious if anyone on here knows if the contents of any of the earlier IndiZone CDs from SGI are posted? A copy of IndiZone3 came with my copy of IRIX 6.2 a number of years ago, and while the games aren't the sort that would impress a modern XBox user I thought they were kind of neat and showed off the equipment and thoughts of the 1995-era, but I also have some earlier SGIs that would be IndiZone 1/2 era. I found a couple lists of the contest winners (but the CDs have more), and an occasional download link, but nothing complete for either. Anyone have links or lists of what was on them?

3 years, 2 months

Systems Concepts SC-4 computer

by lars＠nocrew.org

Anyone ever heard of the Systems Concepts SC-4 computer? "This is an two's-complement 18-bit machine, with 16 general registers and a 16 level priority interrupt system. Its programming ascpects are explained in great detail in the SC-4 Reference Manual, of which a draft is enclosed. Below are times for some typical instructions. Add word on stack (not top word) to general register 1.5 us Multiply general register by memory word 6.2 us Jump 750 ns Push and Jump 1.5 us Compare Immediate 750 ns" >From page 6 here: http://people.csail.mit.edu/saltzer/Multics/MHP-Saltzer-060508/filedrawers/…

3 years, 2 months

Deciphering an odd floppy disk format.

by mattislind＠gmail.com

I have a few 8 inch floppy disks coming from a Q1 Lite computer. I tried reading them on a PC with a Adaptec 1522A floppy controller but it failed completely. Then I tried my Catweasel and dumped the raw flux data. The format differs >from what I have seen before. I did a quick histogram of the flux lengths and it appears that there are four groups of sample lengths evenly spaced. Peaks at 30, 48, 66 och 84 samples flux lengths. The longest flux lengths are interspersed in between more normal flux lengths in the actual data and I get the same type of result regardless of reads of the same track and between different tracks. But the relative frequency is much much lower for the longer flux lengths than the shorter ones. An RX02 (MFM ish) had 26, 41, 55 samples as the peaks in the histogram. As far as I understand cw2dmk software uses 14 MHz setting in the catweasel so each sample length is around 70ns. Anyone that has seen this kind of format before? Or is it just a reading error? I have the same result from several discs though and they look to be in quite good shape physically. Link contains histogram files and a raw track flux file. https://drive.google.com/drive/folders/1URC5i8AsRyP08d_ZhWRovbDp2TMgdj4B?us…

3 years, 2 months

TK70 maintenance--swapping capstans

by cz＠alembic.crystel.com

Well my little TK70 here has been squeaking and it looks like the capstans are frozen/bad. They don't move up and down and they don't spin well. Fortunately I have a dead TK70 with good capstans so I figured I would swap them. Unfortunately I don't have a maintenance manual (does anyone have one?) so I had to figure out alignment myself. Capstan alignment seems to be critical, if they are off the unit don't work... Anyway here is my procedure so far to get the unit to load and unload tapes on the bench. Not perfect, but a start.... Pulling the capstans requires you to remove the two lock nuts on top first. I recommend you count the turns from all the way tight if possible as alignment is critical, and the front and rear ones can be at different relative heights. Anyway if you didn't do this you need to adjust the rear height to trip the optical sensors and the front one to handle tape slew. Note: All the below is done with the unit on a bench, with a PC power supply. The first step is to adjust the rear capstan so the leader tape's wide hole for the end of tape-stop marker allows light from both LEDs/sensors to pass through. You do this by tightening the bolt down till snug, then back off 1/2 turn. Turn on unit, see if it unlatches. It probably will try to turn the tape 4 times then error out. Fine. Power down, back off the bolt 1/4 turn and try again. At some point it will open the latch. Note the # of turns of the bolt then keep going 1/4 turn at a time till it doesn't work again (too high). The proper value for your unit in turns is halfway between too low and too high. Reset the bolt and verify it works several times. For my unit the right height was about 1.5 turns out. Then you need to adjust the front capstan. The problem is if the front is higher or lower than the back you have tape slew errors. Start at the level of the rear one based on the # of turns minus a bit (1/2 turn). Then load a tape. It will load, but when you try to unload things will go bad, the tape will just move forward onto the take up reel 4 times, and the unit will error out. The reason is it has to read the tape as it turns to know a tape is loaded (as opposed to the leader where it looks for the end of leader light). If the capstans are not holding the tape level against the head it can't read. Each time it moves forward a bit, try bringing the front up 1/8 turn at a time. Eventually it will speed up, that means it can read the tape on one of those moves. It should then unload. Now you have the front basically set. It will unload the tape, cycle it a few times to make sure it's working. That's where I am now. Next step is to see if it will read the tape in the computer. I'll work on that tomorrow. Note if you ever shine an led flashlight into a running TK50 or 70 all hell will break loose as the system will see the light on the tape sensor and think it has hit BOT. Even worse is if both LED sensors trigger, then it thinks it is at end of leader and it will throw tape everywhere. Ask me how I know....

3 years, 2 months

WTB: HP 9000-340 memory (HP 98268A), AUI (HP 98235A), SCSI (HP 98658A)

by cmhanson＠eschatologist.net

I've acquired an HP 9000-340C+ and I'd like to kit it out with the maximum RAM, SCSI, and AUI rather than thin Ethernet. Desired: - RAM boards: HP 98268A RAM board (three of them to get to 16MB, I'd probably buy extra just to be safe) - AUI LAN board: 98571-66534, aka HP 98235A AUI LAN Upgrade - SCSI board: HP 98658A SCSI Interface Card Anyone have any of this stuff that they might be interested in parting with? I'm also always on the lookout for an HP 98556A 2D/integer graphics accelerator in case anyone happens to have one that needs a home. That's the integer accelerator with a 68020 and some RAM, which piggybacks atop the 98550A (1280x1024 8-bit color card) via its extra Eurocard connector. -- Chris

3 years, 2 months

Systems Concepts SC-4 computer

by jnc＠mercury.lcs.mit.edu

> From: Lars Brinkhoff > I suppose that main computer could be the GE-645 on which Multics was > developed? And they would still refer to it as G.E. Oh, it was clearly referring to the Multics machine. I assumed that with the GE sale being 1970, by '72 it was not a GE machine anymore. But the MIT Multics site page: https://multicians.org/site-mit.html says the H-6180 was installed in November, 1972; shortly after the letter. Noel

3 years, 2 months

found it: first speech synthesizer (at least, for S-100 systems)

by couryhouse＠aol.com

Have one filed in somewhere with all the s-100 boards... now I have a reason to dig it out! Yes... memories of Wirt's projects! Ed#?? smecc On Wednesday, December 16, 2020 Bill Degnan via cctalk <billdegnan at gmail.com; cctalk at classiccmp.org> wrote: Very interesting Stan. Thank you for sharing this info Bill Degnan On Wed, Dec 16, 2020 at 2:43 AM Stan Sieler via cctalk < cctalk at classiccmp.org> wrote: > Hi, > > Some years back, I was asking if anyone had information about the speech > synthesizer > developed for the Altair 8080 by Wirt Atmar of AICS (in New Mexico). > No "hits". > > Most places on the web claimed the Computalker was first, given the date as > 1976 or 1977. > > (Earlier speech synthesizes existed, but they were external boxes that one > interfaced to, > or were standalone (often with a large/weird keyboard).) > > Today, I stumbled over a fairly bad OCR of Byte magazine from August, 1976 > at > > https://archive.org/stream/byte-magazine-1976-08/1976_08_BYTE_00-12_Speech_… > > It has two articles about speech synthesizers for S-100 bus systems. > > The first is by the Computalker people, who say: > > At the time this article > goes to press, a synthesizer > module incorporating several > detail refinements and im- > provements over the circuits > of this article is being de- > veloped by the author and > associates. > > and > > A detailed user's > guide will be supplied with the > Computalker module > > > Note the future tense! > > The second is by Wirt Atmar, whose product *was already shipping*. > > Near the end of his Byte article, Wirt lists currently available products: > > At the present time, two speech synthesizers > are both commercially available and affordable by > the hobbyist. > > One is the Votrax produced by: > > Vocal Interface Division > > Federal Screw Works > > 500 Stephenson Dr > > Troy Ml 48084 > > Price, approximately $2,000 > > Interfacing: Parallel or Serial (RS-232) > > > The second is the Model 1000 manufactured by: > > Ai Cybernetic Systems > > PO Box 4691 > > University Park NM 88003 > > Price, $425 > > > Wirt had told me (twenty years ago or so) that he thought his was the first > for microcomputers (e.g., a user installed card, not an external box). > Now, I'm sure ... but it was realllly close! > > Wirt demonstrated his product at the earlier MITS World Altair Computer > Conven- > tion, where it won first prize. > > He advertised it poorly/infrequently, since it was mostly a side business. > And, that shows, since history doesn't remember it. > > Stan >

3 years, 2 months

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test-drb February 2021