Hi all, new here. I've been thinking about buying Vince Briel's Micro-Kim kit to teach myself low-level programming in assembler on a real piece of hardware. I know that one can use the serial interface and a PC or PockeTerm to talk to the machine (aside from the hex keypad), but I've also been looking for ways to build/add a video circuit with currently available chips. I'd like to avoid using Propellers or any other modern programmable controllers, and do this the 'old fashioned way'. I found the TVT-6 construction article at http://www.classiccmp.org/cini/mags.htm#PEMags and am wondering if one can still build this. Some research shows that perhaps the IMS5610 could possible be replaced by a PROM of some other nature, and I think this is to hold the software included in the article. The other IC of interest is the 2513 Character Generator, which seems may be replaceable by a 2716 EPROM. I have the .BIN file ripped from an original Uppercase Only 2513 (2kb). The other components all seem to be standard fare (resistors, caps, etc etc). I'm a real amateur with this stuff, so don't laugh too hard if I'm really lost in space here, and am better off with a Replica1 kit. Thanks, folks.

Welcome to 6502.org! And congrats on your ambition to explore Don Lancaster's bag o' tricks.

Frankly, I'm delighted to discuss the topic. Decades ago I fitted my KIM-1 computer with a variation of Don's "cheap video" technique, and a subsequent, built-from-scratch machine carries the idea to another level entirely, not only providing video but expanding the CPU's memory space and instruction set! I found real inspiration in Lancaster's approach to hacking -- my hat is off to him.


Given its resemblance to the original KIM, the Micro-Kim is guaranteed to be a wonderful vehicle for learning. But unfortunately it'll be more difficult to adapt for Lancaster's video technique. That's because the technique relies on being able to isolate the memory data bus from the CPU data bus. The KIM incorporates 74125 bus buffer/driver ICs which allow this. Disabling the drivers prevents memory data from reaching the CPU bus, yet at the same time the memory data can still be separately retrieved from the "upstream tap" mentioned in the Radio Electronics article. In contrast, the Micro-Kim ties the memory data bus directly to the CPU data bus (without first passing through a bus buffer IC). Thus the two buses cannot be isolated from one another.

Naturally there are ways to deal with the issue. You could modify the Micro-Kim to include a buffer IC (a single 74xx245 would do), or you could build an expansion board that included an additional memory chip buffered by a 74xx245. How's your comfort level on the hardware side of things?

Alternatively, I wonder if there's any chance you could procure an actual KIM-1. The Replica 1 kit you mention is unfamiliar to me. I'll report back when I've found the necessary info.

cheers,

Jeff

Jeff -
First, thanks for the welcome

Second, there seem to be a few very different iterations of the TVT system. I'm interested in this TVT-6 design because it seems GREATLY simplified versus the original design that I've seen. The TVT-6 is a small 10 IC, single PCB add-on, whereas the original seems to be a massive multi-stacked-board arrangement with many, many IC's and supporting circuitry. My TVT-6 article refers to tying into pin 12 of the 74125's from the TVT card (VD0..VD7), which I assume is in reference to the technique that you mention. A quick check of the MicroKim schematic shows a jumper, going to pin 12 of an onboard 74ls145 Decoder/Driver IC. Is this related? Perhaps there is a provision for this trick on the MicroKim, but my knowledge of how these circuits work is quite vague. In any event, although I can't really design a circuit, I'm quite handy with a soldering iron and multimeter (diagnose electronic engine and transmission control systems as part of my job) and am confident in building a circuit of most any variety. No surface mount, of course I'm all ears on the 74xx245 buffer hack you mention.

Third, I simply can't afford a REAL KIM-1. Oh, and the Replica1 is another of Vince's creations, an Apple 1 clone with onboard video

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Garth-
You present another possible solution to adding video to this machine. I downloaded all of the old "KIM-1 User Notes" newsletters, one of which presented a simple circuit to use an oscilloscope to add graphics to KIM-1 games. This is another option to consider, even though it would mandate my buying an oscilloscope. Which might not be a bad thing. I like to learn how to use new equipment, and an oscilloscope is useful at work, too, to diagnose ECM/TCM pulse signals. Hmm....

I'd like to learn more about both approaches. Thanks again, fellas!

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Well, in general what I had in mind was that you would locate the eight etched traces which are the data bus, and you would cut them. Then the 8 severed lines on one side would connect (via 8 soldered jumper wires) to one side of the 74_245 -- and likewise on the other side of the '245 back to the other side of the break. Sort of like a detour that you've created in an 8-lane highway. The '245 is a 20-pin chip; you could mount it on a kludgey little daughter board dangling close to the Micro-Kim. Mechanical details could vary.

Is it your plan to copy the PCB layout from the magazine? Notice that the expansion connector on the Micro-Kim (a DIP header) differs from the card-edge style of connector used on the KIM, so again there's a mechanical issue to deal with. But presumably all the same signals are available. (I haven't checked.)

It strikes me that, if you made your PCB larger than required, the '245 and the 6264 ram chip could reside there instead -- it would make a tidier arrangement. In fact, if you're comfortable doing point-to-point wiring, then you could skip the etching and do it ALL point-to-point.

I need to have a very careful look at the magazine article, since I would hate to steer you into difficulty. But one way or another I'm sure this can be made to work.

-- Jeff

EDIT: Oops, I missed Garth's post while composing my own. Love the X-Y-Z display -- nice work!

Honestly I haven't read the article yet. But certainly there are flavors of Lancaster video capable of multi-line displays.

Garth-
The oscilloscope circuit for the KIM-1 I am referring to can be found in the (very rough) scan of issues 9/10 of the KIM User Notes newsletter. Find it at http://www.classiccmp.org/cini/pdf/KIM% ... ol0910.pdf . It wasn't intended for text (I think you're referring to the SYM-1 circuit to display one line of text on the oscilloscope), but for graphics only. Again, your circuit is one to consider, as I'm really only after text display.

Jeff-
Vince Briel claims all expansion I/O lines available to be compatible with the original KIM-1. See http://www.brielcomputers.com/ and look at the Micro-Kim section for a pinout. The schematic for the machine can be found at http://www.brielcomputers.com/files/mksch.pdf . I'm thinking of going point-point wiring on perfboard for my expansion. Not too worried on the interface connector, I can iron that out myself. I see what you're talking about with the 74xx245 chip. I'd have the CPU and RAM data lines on each side and toggle the OE and/or DIR line(somehow) to (dis)connect them? And you mention a second 6264 RAM chip. My TVT-6 plans don't have any RAM onboard, instead using some ROMs and having the display data in system RAM. Hrmm... When you get a chance, check out the two part TVT-6 article at the link in my first post so we're on the same page.

Yet again, thanks much to you guys for helping a newbie through the process here.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Yes -- re: the '245, that's it exactly. As for the 6264 ram chip, I figured on omitting the one on the Micro-Kim board; just leave the socket empty -- the ram on your new board would replace it. (And the new chip might get upgraded in future, so you might as well put in a 32-pin socket, not 28 ).

Speaking of expansion, I'd seriously consider leaving space on your new board for a 65c22 as well. Yes this is the chip featured in Garth's interface, and it's a very worthwhile device to become familiar with !

Huh. I just did an online search for a KIM-1 schematic, and I found this link to a 6502.org page by Ruud Baltissen. He has plans to build your own KIM, so maybe that'll interest you if you have more free time than free cash. Moreover, you could integrate the '245 buffer chip more easily. But I must say, Briel's Micro-Kim looks awfully appealing!

Past my bedtime, gotta go now. Yes I'll check out the details in the article soon...

J.

PS to Garth: do you think your tidy little X-Y-Z circuit could be simplified even further? I'd be tempted to replace each DAC chip with a set of eight binary-weighted resistors. And, since a 'scope is the only load, then the op-amps and the 12V supplies could be eliminated, too.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

After pricing out the components individually, the MicroKim kit @ 100 dollars is actually a pretty good deal. Will certainly build the add-ons myself, though.

True. Plus, it's just so darn cute !!

Just thinking out loud about what display device you might use... Would you simulate NTSC video (per Lancaster) and use a television style monitor? Alternatively, VGA is a (pseudo-)standard that'll likely be around for a long time to come, but the horizontal scan frequency is double that of NTSC, so you'd have to adjust for fewer characters per line or else soup up your Micro-Kim to run at 2 Mhz instead of 1.

As for Garth's video scheme, it certainly has some major advantages -- notably the vastly simpler wiring. That has to be balanced against other factors, of course. The Micro-Kim lacks a 6522, so you'd have to add that somehow. A more serious issue, perhaps, is that the more characters you display, the slower the refresh rate becomes -- and thus the worse the flicker. With a 1 Mhz 6502 and 6522 this could become a serious annoyance -- I don't know. Garth?

Yeah, I guess to build a resistor DAC there would be some fussing involved, although not too bad. Years ago I built a pair of resistor DACs, and had instant success. But that was with the advantage of using a set of high-precision resistors salvaged from a Linotron phototypesetter BTW I see your point about the 12V supplies -- it's really not a big deal to provide those.

-- Jeff
ps -- going out of town for a coupla days... Might not hear from me

Jeff-
I suppose I'm open to using any video output method. I like the NTSC output because of the nostalgia involved (the first computer that was MINE was a C64, already 10+ years old at that point, using my TV for output). VGA is nice because I've got a spare 14" VGA LCD monitor lying around that I could dedicate to the machine. I guess it boils down to 'what type of circuit is the simplest to build and understand'. Garth wins out here, but as noted, it requires a somewhat non-standard output device (oscilloscope). This adds a bit more cost to the equation.

Still reading, re-reading, and re-re-reading the TVT article and researching the IM5610 function and 2513 replacement. Talk to you when you get back!

Each of these can be replaced by an EPROM.