Inside the 1977 KIM-1: CPU, Video, RAM, ROM and more!
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- čas přidán 28. 08. 2024
- Dave disassembles the oldest home computer on eBay, the venerable 1977 KIM-1 system, and explains what each of the boards does and how the backplane interconnects them.
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That 276- part number is a Radio Shack part number. They made a number of prototyping boards of various shapes and configurations through the 70s and 80s. I remember hand wiring quite a few boards much like that little IO expander and considerably larger and more complex. I'm sure thousands of other hobbyists did the same in that era.
Wonder where we would be without Chuck Peddle. I love the content Dave! I was an unusually recluse, but curious child growing up. Your channel has brought me nostalgia for late middle 90s-early 2000s. I always look forward to your videos!
Maybe the cat would have seen more use, or maybe we got more 6500 systems, or the 6809. That would have been kind of sweet. I love that chip. I bought the color computer just to program on that one.
On the local regulation power distribution scheme: In those days the chips were drawing a fair amount of current on average, and spikes (glitches) when they switch. (hence all the bypass caps). Now if you try to send 5 V through the backplane bus, you are flowing that current, and the glitches through a bunch of skinny traces, wires, and connector interfaces, all of which add a milliohm here, ten millohms there, and inductive impedance all over the place. (any and all wires have inductance)
Mr. Ohm tells us that when you flow current through all that resistance and impedance you are going to get voltage drop. If this voltage drop becomes excessive, then one or more chips becomes flakey. Maybe it only happens on a read if all the data lines change state at once, or maybe it is temperature dependent...flakey hardware will drive you nuts trying to track down the problem.
Now all those little caps will help a lot with glitches. They limit both how much voltage change a glitchy chip puts on the power rails, as well as softening glitches from the neighbors so the local chip is less likely to be influenced by those glitches.
The voltage drop due to average current consumption can't be addressed by capacitors, because they only deal with transients.
Say the current load on the power bus is enough to cause 1.5V of drop on the 5V rail and 2V drop on a 12V rail. Well, the 5V rail dipping to 3.5V is a problem for a couple of reasons. First off, the chips just might not work at such low voltage, or work at reduced speed. But even if they would work fine on low voltage, you have the issue that the cards nearer the power supply (electrically, if not physically) are seeing far less drop, so maybe they are running at 4.5V. That means that their high logic outputs are sending very close to 4.5 volts out to those distant cards that have only a 3.5V supply. And the chips won't like that AT ALL!. Driving inputs (or tri-state outputs) above the supply rail can cause a host of evils. If the difference is less than .5V it usually works OK, because it takes about 0.6V to overcome the junctions that are trying to protect against this.
So you want the all the cards to see the same supply voltage. The method of achieving this on your boards is local regulation. The cards are supplied with a raw supply of, say, 18-20VDC. The same rules of voltage drop apply, and because the 12 and 5V current both flow through that supply route, the drop might be as high as 4-5V. So you end up with 13-14V at the farthest card. The local regulators drop this to putch-near exactly 5V and 12V on the cards, and life is good. The local regulators compensate for however the raw supply voltage varies. The other thing is that while switching regulators technically existed in those days, they were exotic beasts, and you needed a true guru to make one that worked at all, and a freaking magician to make one that worked well. So all the early computers used linear regulators, which generate a lot of heat. By putting lower power regulators on each board, you spread that warm warm lovin' over lots of area, which lowers die temperatures, which keeps the smoke inside the regulator pass devices.
We had to do the same thing when I designed a board for the DEC Alpha. That sucker needed a ton of current at 3ish volts. So we'd put 5V on the board, and that fed a voltage regulator that lived right next to the processor. Pretty sure all the really fast processors still have to do this.
A great response but there's a much simpler answer. The 3 pin linear voltage regulators of that era had limited current capacities to a max of 1.5Amps (without having to resort to additional circuitry & finding real estate to centrally dissipate the heat) thus it was much easier to use a relatively inexpensive simple high power step down unregulated power supply comprising of a step down transformer, diode bridges & a few giant filter caps to provide bulk power & then decant that power to feed the lower power voltage regulators on an as needed basis.
The distribution of +/-12, +/-5 & +3.3 volts isn't an issue, with the correct conductor sizing & layout its distribution works just fine. It's done ubiquitously including most IBM PC compatibles and other systems. Some of today''s GPUs draw over 500 watts in this voltage range! Today's CPUs use voltages as low as 0.9 volts @ incredible current; thus for now the voltage regulation is done adjacent to it.
As for the little caps, these act as Coulomb buckets acting as local energy reservoirs (like local batteries) rather than a bypass or decoupling function; they're there to cater for poorly designed power distribution networks (PDNS); they'd be sprinkled willy nilly in the hope it'd address system stability (& unfortunately the willy nilly sprinkling still continues!). These days a properly designed PCB does not require the little caps; in fact they can be useless for today's designs because the very fast transition rates used where the signal can't even reach them.
@@PebblesChan There were 5A regulators available from National Semiconductor, in a TO3 package, with a pretty high per unit price, that needed a fair chunk of aluminium to get that 5A out of them, even with the minimum input output difference of 3V, thus the 8V supply rail, that was 8V fully loaded, to 10V unloaded. 15 to 30W to dump on a card was hard, you had to either have a heatsink, running the full length of the card, with fins that took up another card space, or have it take up half the card space and still get a card in next to it. Or have a cooling fan directly cooling just that frame section. S100 bus simply did it the easy way, need 5A, put 5 1A regulators on the top of the card, each with a heatsink to handle 6W, and have 5 Vcc bus rails to the assorted chips, so each rail was only loaded to just under 1A. Easy with TTL and NMOS, as power use really did not change much with clock rate.
Cray did it even simpler, as ECL has a current use that is almost constant, irrespective of clock, so all they did was to have a single ferroresonant power supply that used massive copper busbars to deliver the -5V2 to the cards, with absolutely no regulators at all, just a ferroresonant converter that made a constant AC voltage, and then simply tossed in a massive set of rectifier diodes, and truly massive capacitors to smooth out that supply. Then used liquid cooling, to keep the chips on the card frames from melting themselves off the boards. No regulators, and a variac with autotune to fine tune the voltage.
@@SeanBZA Absolutely & thanks for the great reply! That's why I specifically said 3 pin meaning the TO-220 package. (The TO-3 has only 2 pins & uses its case as the third contact). 10A TO-3 versions were released later but were even more expensive. My S100 system is powered up right now! Its 16K RAM cards has what you said - they've each got 4 x 5V TO-220 regulators - one for each 4K bank. A quick count of the voltage regulators in my system is 24!
Modern CPUs are so power hungry that they get their own 12V link from the PSU, and have their own regulators right next to the socket.
@@PebblesChan Those TO3 were later on also released in TO247 package, which had three pins.
So many bypass/decoupling capacitors :)
Every IC needs a 100nF capacitor as a friend.
I love the Mercedes wheel "table" cool blend of Top Gear, Roadkill and Curiousmarc. Your videos are awesome, btw!
I think it was 1976. My school bought a Wang computer. It had: 12k ROM for the OS and Basic interpreter, 8k RAM, two 128k 8 inch floppy drives, input console CRT monitor and keyboard, mark-sense card reader, dot-matrix printer, letter quality printer (looked like an automated IBM Selectric typewriter). The whole thing cost $25k. We had to sign up for time on the computer after school hours. It was a lot better than shipping off mark sensed cards to be processed overnight on the one IBM computer in the school district. That was state of the art at the time.
A few years later Wang started selling expensive "word processing" machines to businesses. My sister used one at work and it took me no time to figure out it was just a standard CP/M machine running standard Wordstar with off the shelf components like a daisy wheel printer.
There is another CZcamsr that rebuilt a wang word processor
Personal Computing in the 70’s is a lot more of an extremely advanced home electronics project than it is what we’d recognize as computing today or even what’s considered computer use in the 80’s
Dave, you did a fantastic job of production on this one, crystal clear, and you did an respectable clean up job on the top layer to show off the mystery chips!
The architecture, with the backplane layout, seems quite sophisticated and forward thinking for the time. Just fascinating!
Was watching an interview with Steve Furber, the main designer of the BBC Micro computer and original ARM chip, and he brought out a lot of his university projects from his time at Cambridge made around the same time as this, and they were all very much the same. I think it may have just been the standard of the time.
Backplanes were exceedingly common in minicomputers and mainframes! :) (And still are in some cases, otherwise clusters of smaller technically-microcomputer nodes are often used instead.)
Those white pads become conductive as the rubber begins to age and deteriorate. I have seen them add resistance and even shorts to the PCB. Remove and clean the surface to save yourself headaches.
Thanks for the info!
Dave you seriously have the best background music. Your videos are both entertaining and soothing at the same time. Best way to end the day.
interesting seeing the in-socket bodge wires on that last rom/prom board.
I got a KIM-1 as my first computer back in 77. Added a 4K memory board and a TVT video interface. Then eventually expanded it to 64K with video card (80x24), rom based monitor. Never got around to adding in a floppy disk controller. Still have it, but had to replace keyboard so it is no longer stock. I did end up building my own CPU card to replace the KIM one on my home built machine.
While the disk controller may have been intended for 8 inch drives, that NEC 765 chip was *very* widely used for many years and that included plenty of use with 5.25 inch drives. The compatibility is going to be down to the software drivers and other hardware considerations, including whether the disks were intended to be soft-sectored or hard-sectored.
Oh, and that hand assembled board - could it have been an early SASI/SCSI host adaptor, or is it too early for that? Maybe for some kind of tape drive? I didn't get to count the number of ways in the ribbon cable. And that's not wire-wrapping - that's pretty standard hand soldering for digital electronics in the late 70s - early 80s. If you're a hardware guy, that's a pretty simple board to wire up. For wire-wrapping, you'd have IC sockets with very long square cross-section pins, and the wire is wrapped very tightly around the base of the pin for 8 - 10 turns for each connection, using a specialised hand tool. The tightness of the wrap ensures a good connection, such that no soldering is then needed. (I still have a hand powered wire-wrap tool in my box of 80's stuff.)
Last thing - you're not the only guy that straightens out decoupling capacitors. It's a "not quite OCD thing" for me too. Just be careful with those older ceramic disk caps - they don't like the leads bending close to the capacitor body since it can fracture the coating and then moisture can get in which doesn't do them much good.
The KIM-1 was way too early for SCSI. I can't remember if SASI was around at the time, it may have overlapped slightly. I'm very doubtful about that being any sort of disk interface. It looks to me like a pair of 8 bit latches that perhaps will make up a 16 bit bus on the end of that cable, but I think that would have been way too slow to interface to a disk drive at the time. Remember the KIM-1 only runs at 1 MHz. I'm guessing this was an interface to some special external hunk of hardware the original owner had. Maybe an early automated juke box or the like.
Awesome video. Much like looking at the Wright brothers equipment in their early days of flight. Very cool thank you. Take care and peace out!
Love that wheel table! :-) Thanks for continuing the KIM videos, this is so interesting!
Nice tabel tire with glass :D love the Mercedes logo under.
Thanks! Those are my winter tires! I bought the rims on eBay as a nice discount so I don't have to swap tires on rims seasonally... so I make a table out of them!
@@DavesGarage Thats Cool :D
Brilliant visuals and narration! Thanks
Nice one, as always!
I would love to work just one day in Dave’s Garage. It’s kinda a bucket list item of mine.
God Bless.
Very cool video but I have to say that the pronunciation of "bodge" is... unique. 😉
Remarkable machine. I can't even imagine how I would approach designing something that complex. I suppose the modular nature would help. Still. Very impressive.
It's all about the modular nature. They had the S-100 and S-50 busses. Different companies could make cards that would be compatible. Actually exactly like PCs now, but more fun! Yeah each card minds it's own business, a RAM expansion card keeps an eye on the bus for RAM accesses and answers if they're in it's range. A serial port card sends out serial data to a peripheral, when the bus writes to it's address. If the bus reads it's address, the serial port card will place on it the last data it received.
Each card tends it's own garden and is ignorant of the rest, by design. The CPU sits on there and sends out it's read and write requests, knowing that they'll come in (or go out) over the bus, put there by whichever card bears that responsibility. They all have their own address ranges to respond to, they all watch the address bus and react when it's their time to shine.
They must have done a pretty good job to allow cards from different companies to work together, forming a working computer. The theory is simple, as is the practice, if it sticks to the theory! I suppose getting stuff to work, when it ought to but didn't, was part of the fun, the feeling of triumph it'd give you when you succeeded. You can get the same feeling now by trying to connect cheap Ebay security cameras up to your Wifi.
@@greenaum I think the serial protocol must have been key to that. I think it was standardised pretty early so that all the components could speak the same language.
But just the idea of designing something so complex as a computer.... Without a computer to do it on..... Mindblowing lol
Those EPROM chips with the windows in them get erased using UV light. Might not be a bad idea to put something over the window to prevent them from getting erased by mistake.
5 and a bit floppy write protect stickers were perfect. Sticky as doodoo, metallic, and just the right size. Many of us that came from the BBC micro with its 'sideways roms' (bank switched) had eprom programmers (and windowsill erasers (in summer) (nested parenthesis?)) just reached for the sticker sheet in the verbatim box and felt safe.
I was watching a video from low-spec Hardware about early microprocessor creation. There was a part about MOS company ordering chips from a manufacturer we're all the chips were made the same. They then had to come up with the lithography to map the connections, and bodge wires having to be put in place after the fact was very common. I don't know if it helps, but there may be some useful information in those videos. Specifically those about Commodore, MOS and Spectrum.
Whenever I see you have a new video, Dave, I usually say to myself, over dramatically, WHAT? WHAT?!" The next 12:48 of my life is set in stone.
FYI "bodge" is an Australian term for fixing something in a very messy or hacky way, i.e. bodge job. We pronounce it boj, like bog but with a j sound on the end instead. Loving the classic content!
In Byte Computer magazine (Volume 4 Number 9, September 1979) there is an article called "Interface a Chessboard to Your KIM-l". If you can find a copy it is an interesting read and was written by: Jeff Teeters. Mr Teeters made a chessboard with a load of wires which he fed into the Kim I in order to program it to play chess.
My first guess is that the prototyping card was a parallel interface for a printer? Although it could’ve been for something like a paper tape reader, but that would seem kind of pointless since they apparently had a disk drive connected. I’m pretty sure that same 765 chip is also compatible with 5 1/4 inch Shugart drives. That chip was used on the original IBM PC/XT floppy controller.
Those bodges might actually be intentional. Those are probably only two layer boards with no internal layers. They might have used wires to create the intended circuit when there were traces they couldn't resolve during layout because of topography and space constraints. You'd need to draw the schematic to know for sure.
Wouldn't you design that into the PCB though? Some PCBs, especially single-sided, have jumper wires, but they're part of the circuit, have their own pads and holes. These bodge wires are just tacked onto the bottom of component pins. You wouldn't design a circuit like that, it's unreliable and you have to pay somebody to solder all the wires on, and to get them on the correct pad out of hundreds, every time.
Users cutting traces and adding patch wires was the done thing back then, when it was much more amateurish. Like Dave said, your "update" might be a sheet of paper telling you where to solder some new components. Cutting a trace here and patching a wire there fixed mistakes with the PCB, but it also allowed customisation by the user, which was very popular. I doubt there's many pre-1980 computers that don't have a few cuts and patches here and there.
@@greenaum again, we'd probably need to see the schematic. Layout was done by hand and depending on the network, they might have needed to run traces which crossed each other in a topography they couldn't route with traces on a 2 sided board. Not only are you passing data lines, but you're a also running power and ground to each of those logic chips. Running additional wires probably wouldn't have been the first choice, but I can imagine that it might have been a limited choice. Even if you could have used vias to route a signal around blocked paths, that might have been more expensive and less reliable for a given route.
@@R.B. I get what you're saying. My point is, that wires, which certainly are used for reasons like you say, would be given their own drilled pads just like every other component. Bodge wires are only put in at the factory when they've already manufactured the product, or at least the PCBs, but then discover some mistake. Rather than scrap all that, they can use bodge wires.
@@greenaum fair point. If they were intended, they almost certainly would have had their own pads. That's enough to convince me that they are probably bodges instead of designed from the start.
This medley episode reminds me of the showcase segment of the game show "The Price is Right"
At 11:10 one of the ICs has a pin bent outside the socket. This is always interesting, if it's a TTL input it should pull itself high. If it's an output it has been isolated. I've used this technique many times over the years to help troubleshoot.
Likely this is a cheap dip switch equivalent for setting a configuration option on the board. I'm guessing it might have been part of board address decoding. It wasn't too unusual for hobbyist boards in that area to use this technique to set configuration options.
You can probably use a PC AT 5.25" or 3.5" HD floppy drive instead of the 8". Might require some software changes, and cabling changes but nothing really rocket science.
Proto board is a printer interface maybe?
I absolutely love seeing an actual, physical KIM-1; and it's being used! I had a KIM-1/COSMAC ELF emulator on an old PalmPilot. Pretty much only used it to play Star Trek.
My computing experience began with the KIM-1 & would go on to be an application & database developer
The little protoboard is point-2-point wired using what looks to be enameled wire. During soldering the enamel is burned away allowing the solder to connect. Wire-wrap will have long pins on each socket pin (.5 to 1 inch) with wire literally wrapped around the pin. Several wires can be wrapped to each pin using a tool specifically designed for this. The pins are square, the square edge cuts slightly into the wrap wire creating a gas tight connection which is why then don't need to be soldered. No available free oxygen means no corrosion. The 8212s are 8-bit parallel port I/O chips. These may be two output ports, two input ports or one of each. It is most likely mapped into 2 memory addresses. As an output port the data is latched, so a memory write to the address would result in the written byte being latched on the output pins. For a memory read cycle the 8212 will take the 8 input bits and present them as a byte to the processor. You are correct that it looks like a 50 pin ribbon connector was used with an edge connector at the end that could have been used for an 8-inch floppy drive. I suspect whoever wired this used this cable as it's what he had on hand.
Cool, thanks for the explanation!
Computers had to start somewhere but 😳 holy crap that's a lotta chips and dips and wiring!
I love this series. Excellent work.
I think the home-brew board is just general purpose IO....... a "user port".
Nice touch, having the Pet Space Invaders demo in the background.
On the last board, those looked like UV erasable EPROMs. The lenses should be covered to prevent unwanted erasure. After all these years, I would not be surprised if you find them essentially blank.
Recently I read some docs for the 27c series, they state that data can be expected to last about 20 years on the chip, when properly covered up, so there's some chance that these would need to be rewritten even if covered.
Adrian Black had worked with some 8" floppy drives from a TRS-80 Model 2. He may be able to help.
Yeah, but he doesn't seem to respond to Dave's requests for anything unfortunately. :(
Those 8-inch Shugart drives are quite reliable.
Take the old 60’s “Sugar, Sugar” song by The Archies and replace it with Shugart.
Shurgat, Shurgart
Oh, honey, honey
You are my data store
And you got me wanting more
I was a fool that bought an original Macintosh. Memory upgrade involved soldering chips and wires directly to the motherboard. It wasn't an official Apple upgrade - there wasn't one. But the mod worked well enough.
That card built on the perf board, given their I/O chips - perhaps a parallel board?
Re: the 8” drive, perhaps Adrian has something that you could at least borrow? (Not sure if you know/have ever spoken to him mind you)
I think Dave said he tried to contact Adrian earlier, but got no response. :(
One Item on my computer bucket list (close to the top) is to build a Kim1 as close as I possibly can to the original, modern repro's remove too much like the edge connector. It will probably spend much of its life as a wall hanger but it will be all for fun..
This is all from the era when I got started playing with micros. I know where my mc6800 toys are but I'm not sure where to look from my 6502 parts. This could be fun. I still have a few 8" floppy drives but I don't know if they work. Maybe I should bring one back online.
This is such a cool series, I love looking at things like this. I've got an S-100 system that I'm trying to get working, but it's a mid-80s unit.
I actually have three working 8" floppy drives, but I'm afraid I can't send any to you since I'm actually using them for my own project, haha.
Two go to the S-100 system (it's a Compupro 8/16), and one's been set up to connect to a PC so I can read and write disk images. They all came off eBay though, so I'm sure if you start watching you can eventually find what you're looking for.
You may want to check out Tech Tangent channel. He just got one of those systems and a IMSAI 8080
8:26 276-152 sounds awfully like a Radio Shack/Tandy catalogue number
That hand made board might be a copy of Apple 2 disc controller to use Apple 5.25" drives?
The hand-made board might just be a general purpose I/O board, for connecting up to electronic projects, or maybe interfacing (with suitable circuitry) to Ham gear. Maybe it was to control robots. It could also be a printer port. But simple I/O boards were popular enough back then, could be that, the owner quite probably had an electronics hobby as well.
CNC machines used to use paper and mylar tape to store their programs to produce parts
Sup Dave? Good job as per usual. Very nice DIY project there. And actually, my big question is what OS you shall be using with that rig? (perhaps some scratch-made machine language, I've no idea) Looking forward to further developments...
MS-BASIC v1.1, if you can call it an O/S! There is a DOS for the disk controller of sorts, if I get that to work!
Dave, having spent some time with Gov't projects that I can't speak of... that other interface harness was probably for a tape drive. This would have been something that looked like a lady's train case (luggage) with a cassette player in it. They were used often on the Data General Nova 3 or 4 and some Digital (DEC) boxes from the Early to Mid-70s.
Did you get the Mach-10?
Yes, either tape drive, or for a printer, using a modified IBM golfball typewriter that would provide output.
@@SeanBZA the Kim-1 had a tape drive built in, so probably not that
I also had a KIM1 from 77 to 79, but I didn't get the idea to build something more extensive from single board computers until 1980 with the dividers that Sinclaire had.
Wow, those memory chips are beautiful! And the amounnt of decoupling?! :o They must be hungry ! :D ps. those green wires are not wirewrap, they are enamel wire, the green stuff is either scratched off or burns off when soldered.
As a Plummer, I bet you're good at preventing leaks; maybe that's why MS feel safe entrusting you with their source code :p
Dave, you might wanna put some stickers over those EPROM windows. Over enough time, even ambient light can flip a bit or two. Ideally get those nifty ones with the metallic backing for complete blackout.
BTW where'd you hear the word "bodge" pronounced like that? It's supposed to rhyme with "dodge", every time I've ever heard it.
UM if i am not mistaken, those 4 ics with the gold window frames look like the old style eproms that use UV light to wipe or delete anything on the IC and should be covered with a sticker.
The D765C was also used in the original PC, so it is also usable with 5.25" and 3.5" drives, only the software could be the limiting factor here.
Are you taking any kinds of antistatic precautions? I haven't seen a wrist strap or static dissipative work surface. Static may not destroy the chip initially. It may however cause metal to move in a via on the IC, on the bonding pad or even in the bond wire. (electromigration). Current flowing in the weakened area as the chip does its normal work causes more metal to migrate and eventually it fails. Electromigration will eventually cause all chips to fail assuming something else doesn't kill it first. Heat softens metal making it easier for the metal to migrate (keep your ICs cool).
Very cool coputer. my guess as to the hand wired board is that it's for a parallel printer port. Or maybe just an I/O port. Can't wait to see more.
That upd765 is a standard floppy controller used up until the 80's. It will handle 3.5" and 5 1/4" DSDD floppys ~720K. Don't think it can do 1.44MB or 1.2MB HD disks. Amstrad used then in their CPC range with their weird size 3" disks but standard drives were compatible.
Seeing all those boards reminds me of the time that I found a video card and couldn't figure out who made it. I remember running MS-DOS and running the debug command. I believe the command was d 0000:00CD. It displayed the memory contents and it's ASCII code. It would be cool if you could talk about how to use some of those old dos programs to really get to the bits and bytes of the hardware.
Bodge wires implies a fix was required due to a design failure. Mod wires implies a revision to improve timing, change clocking on faster chips, decode addressing for larger eproms etc.
For someone who spent years moding boards to later revision levels as a field engineer, you are disrespecting the time and effort design engineers went to to improve the products at a reasonable expense rather than state a serviceable board needs to be replaced each time improvements were available. In a time of rapid development, changes to hardware were issued frequently, and if you find a board from the era without mod wires, it might not be a better designed board, but one that needs mods it has missed out on.
That last board has quite a range of different things on it, so it's probably more or less a computer on its own. In addition to the 6820s, there's a 6850, which is a serial ACIA, implying it's meant to communicate with something.
I'd love to see the circuit diagram for that video interface, and see it up and running!
Very nice purchase. That bottom board seems to me to be the most intriguing. If it is an EPROM burner, then maybe that is how you installed software so that you didn't have to load it from disk? Burn it to EPROM and then move it to one of the empty slots? Seems like a nice feature for back in the day, not as convenient as a disk drive but load times would be non-existent. Does this system do any sort of bank switching or does everything have to map into the 65536 bytes of the address space? Do those EPROMs still have any data on them with their windows open for this long?
Love this channel
Also can you do one on reading those weird symbols on ceramic capacitors.
The EPROMs are 2708s. There looks to be enough hardware around the ZIF socket to confirm this is a programmer. VPP controlled by a switch isn't uncommon. These typically worked by reading a block of RAM and writing those bytes to the EPROM. An assembler might load the assembled code into RAM for testing/debug. Once you are happy you commit it to EPROM. The empty sockets are for additional EPROMs to be added. The ROM sockets will be someplace in the memory map. I'd guess you will find a more advanced monitor in these ROMs that includes the code required to initialize the disk controller IC and to load the IPL code from the first sector of track 0 of the floppy disk into RAM. That IPL code is then executed to boot the system by reading the OS from the disk into memory. In the S100 / CPM world this is how CPM gets booted and I'd guess what you have is very similar. The code to work with the video card is probably also in the the ROMs. (Basically a monitor/BIOS in the ROMs). Total guess work on my part but based on what I see and how things worked back in the day it would seem logical.
Yes, and the 2708 is, like all early EPROM chips, in need of a substrate bias of -21V, and also is programmed with 25V on the program pin. Can be left on for program and verify, but really not a good idea to have it present on power off, as you will find some random locations get written to logic 0, often only a bit or two along the line. They get really unhappy, and refuse to work, with that substrate bias missing, but generally, other than not listening to the address and control lines, do not often blow up.
Just a note - those are 8 k bits, 1k by 8.
{^_^}
If possible, you should check the unregulated voltage under load. If its dropping a lot of voltage, then I’d consider adjust/replace with a regulated power supply with a matching voltage. Just so the voltage controlling devices are trying to dissipate to much Wattage.
I would back up the eprom and cover the erase windows. You risk losing the firmware from studio lighting.
Thx for the vid… nice Submariner:)
that edge connector suspiciously looks like the edge connector from a 5.25 inch 1.2 mb floppy drive like came on an ibm 8080/8088 workstation. its probably a custom controller to use a more up to date drive than the original 8 inch drive it originally supported.
Do I sense a Dave's Garage/CuriousMarc collab in the future?
I live about 15 miles from WDC.They are still in business.
There's also a 6850 UART on the board next to those two 6820s.
Cool project. One thing… “bodge” rhymes with “dodge.” Sorry if I’m missing a joke….
This is a wonder amazing
Dave I think most of the stuff you showed kinda matured in XT days to a motherboard and different expansion cards like disk controller floppy/hard MFM/RLL and serial/parallel cards...
PC went a long way
The left most chip on the main board is in the "wrong" direction. This would have been very hard for me to design something like that.
Apart from that, I really like these old computers. It's almost like they can be understood to the last (literal) bit. Compared to the hyper complex stacks of layers virtualization we have today.
ok, @5:58 that was pretty funny
The mystery board. Could it be a homebrew GPIO interface or similar?
Hello software Dave this is hardware Dave. Just to help with some ideas, if any of those windowed eproms have programs in them, I would suggest you put a double layer of electrical tape over the window as just regular sunlight can actually erase those over a number of years. That board that you thought might be a disk controller could be a scsi or sasi interface. the scsi interface has several address pins for which device you want to talk to and then it uses a bidirectional bus. Sasi is similar. You can probably look up the connectors for scsi and sasi on the internet. This is just an idea to point you in a good general direction hopefully.
SCSI wasn't standardized until 1986... (X3.131-1986) So 10 years after the KIM 1... launched in 1976.
I left a comment here. Likely a tape drive interface like used on the Data General Novas.
@@ramosel Maybe for SCSI as an industry standard, but SASI was in use by 1980 at least as a standard way to interface to hard disk and floppy disk controllers. I debugged more than a few systems in 79-81 using that interface.
@@GodmanchesterGoblin And the Kim 1 was out in 76... if you remember, the first S in SASI was Shugart. Dave Already mentioned a disk interface and he’s looking for a Shugart 8.5” floppy. Boucher developed SASI, from the beginning (1979), on a 50 pin ribbon. Early tape reader cables were often discrete wire harnesses that had twisted pairs or braids owing to noise issues from the drive motor and solenoids in the mechanism. I’m not saying, it WAS/IS a tape controller, just likely. KIM 1 was years before dual disk drives or diskcopy would become general practice.
@@ramosel I was making the assumption that the hand wired board was later. A system such as this was likely put together and enhanced over quite some time - that would be normal in the DIY community. But you may well be correct about the tape drive possibility.
@@GodmanchesterGoblin Good point. That board very well could have been later.
@08:09 the upper left chip has '1400' labelled on it. Could this possibly be a baud rate? could the connector be for an older tty terminal or 'tv typewriter' instead of a disk or floppy drive?
just my 2 cents.
Love Dave, who wouldn't? That said, there was just a tiny moment in this video that he sounded like Yogi. But, then, we all know he is smarter than the average bear!
DIP package???? Right up there with ATM machine.
That homebrew card, could it be a printer port?
You really don't need a lot of electronics for a floppy drive controller if you do everything in software. Ohio Scientific's controller from that era was just a 6821 to move the head around and detect the index hole and a 6850 to read and write the data.
Did you get your hands on a Shugart 8 inch floppy drive? I got one that is new old stock that I have no use for.
That little board.... 2x 8 bit user ports?
Looking at the custom board, is it possibly some kinda serial board, like a rudimentary network card for connecting to a terminal or teletype?
Yeah, okay. But what's the story on the Mercedes-AMG rim with what appears to be a winter tire? ;-)
Could the half size board be a parallel (ASCII or matrix) keyboard connection? Since you've got video out, and disk, it would make it a 'complete computer' without need for a terminal or teletype.
The "bowdge" vs "bodge" wire pronunciation?
Beware of the horrible TI IC sockets!🤢
Cover your eeprom windows!
Perhaps impertinent of me to ask but ... if you pronounce Bodge like that Dave how do you pronounce the car manufacturer "Dodge"? Never heard that one.
Is it intentional affectation that my spectrum brain is completely missing?
Ah, but there are many dialectical differences. Celica, Nike, Sporage, all different in Sask! I honestly always heard it that way probably from someone who read it in a book. It was a small town!
French Canadian or Metis influence?
@@DavesGarage I love it. I shall Bodge with impunity from hereon. At least you don't murder "Deprecated". Be well.
@@DavesGarage Before I asked I went off and checked the Canadian pronunciations of "Dodge" but couldn't find a reference for Bodge. Hence the question. Spectrum? No.....
👍👍!
Is boage wire the Canadian pronunciation of bodge wire? I've only ever heard it pronounced "bodch".
7:55 bankswitching logic?
or gpio port
"If there was anything that Bill Gates taught me, it was was never to namedrop."
🤣🤣🤣
He's done it more than once before if memory serves....
@@GodmanchesterGoblin But Bill Gates actually responded to one of Dave's videos, if I remember what Dave said a little while back. So while Dave actually met Bill as a relatively new employee, I think he has the right to joke about namedropping now & then. ;)