I think that TTL is eventually going to go by the wayside, unfortunately. I mean, yeah, we still have 74-series, but using 74ACT circuits in a board designed for 74LS just won't work. And who knows what will come on down the road?

I lack CPLD or FPGA capability. If I had even moderate CPLD capability, I wouldn't have to put up with 160x100 video resolution for the Kestrel 1.

The other problem I have is soldering the damn things into a circuit. I'm still not convinced that CPLDs are hacker-friendly in ANY way. I'd have to etch a PCB just to play with the damn thing, and PCBs are DAMN expensive in small qtys.

And then there is that small issue of voltages -- most modern CPLDs are 1.8V to 3.3V devices; attempting to use them in a 5V logic design, such as the Kestrel 1, will be nearly impossible without expensive level converter chips.



Anyway, what I wanted to say originally was, if you wanted longevity of your circuit, I think the best possible way to achieve it is to include the equivalent schematic or the raw Verilog/PALASM/whatever source code for the design. That's the best possible way I can think of to ensure easy workability for the future.

That way, you leave the choice of future technologies open.

I ended up taking a page from the WDC development board and looking at the Xilinx XC9572 CPLD. It has an 84 pin PLCC package, so a socket is easy, it has .100 pin centers. It is like a smaller gate count version of the XC95108.
I used ExpressPCB for the first board revision, and I am using it once again. I have made changes in the design to make it much more generic and hacker friendly. You download the circuit layout and send out, cost is maybe 50 dollars or so for each, cost dropping for more. Ri9ght now, still job hunting but when it comes time, will make a couple and sell at my cost or something.

The one thing I REALLY REALLY like about using CPLDs is for a finished board, the logic paths can be changes by the reprogram, and it can be done multiple times. This way, instead of having to hit up cuts and jumpers on the board, it is a firmware change on the CPLD.

I already have a monster video card planned for this as well that can easily be run from the 6502. It is almost the same as the Elm one, but with 6502 based differences. For the job, I was planning 3 seperate video sources on a single external board, but that no longer matters now.

The XC9572 is $6 in quantities of 1 at Digikey, and the XC95108 is 12 bucks.

software is free ISEpack at the Xilinx website. 800 meg download or so. Programming cable is 20 bucks from Diligent. Programming port is 6 pin .100 center connector.

so overall, not a bad set of beans.

_________________
"My biggest dream in life? Building black plywood Habitrails"

That's precisely my point -- $50 for each PCB. And if you screw up, well, oops, you're out $50.

And since I'm totally new with programmable logic, and since $50 is a *LOT* of money for me, I'm probably going to go with a solution from Xess. (specifically, I'm thinking of using http://www.xess.com/prod034.php3 ) Although it costs $160, it's pre-fabricated, relatively easily programmed, and has 64 pins or so of I/O that I can couple to various external goodies.



True -- but I'm talking about things like, for example, where I discovered the clock slew rate was too slow on my Kestrel 1p1 and 1p2. That type of thing cannot be fixed by reprogramming the CPLD.



Funny -- after researching the Xess board, I'm planning on the following:

* Paging-capable MMU -- yes, Virginia, this system will support true virtual memory and memory protection!! Theoretically, if someone wanted to port it, it will run Linux. Since the CPU itself can only address 16MB of RAM, and the board has 32MB on it, I figure an MMU would be needed anyway, so might as well make it useful!

* Video architecture inspired by AGNUS and DENISE, but with some elements of ANTIC thrown in (like, a *slightly* richer Copper instruction set. ). Expect a minimal blitter as well.

* Audio architecture that is a mixture of PAULA and SID, or as close as I can come to it. It should have some amount of built-in synthesis capabilities, plus the ability to play waveforms from RAM.

The highest priority is the video architecture, of course, with the MMU being very close second. Audio, I'm not so concerned with -- that can be offloaded to a handful of ATmega chips, I think, via dedicated SPI links.

Thats why these chips are really the future. Also, the XC95108 has several voltage versions, incvluding 5 volts which I will be using.

The first rev board I did with the 134 cost 50 bucks since it was an odd size because of the slots and everything. I do think it was possible to squeeze it onto a standard sized 51 buck for 3 special, but it would have been insanely tight. I wanted some room.

The rev 2 board is more of a trainer to give away and sell. The CPLD will be reprogrammable for various functions, I will give how to do it and all. Never done it yet, I only did a reverse engineer on one for the sake of schematic build. But it looks perfect as the element required.

The XC95108 is nice as it fits into a PLCC socket, so a nice socket with .100 centers is easy to deal with...

_________________
"My biggest dream in life? Building black plywood Habitrails"

I had some test boards built for the Xilinx XC95108. It Includes pads for a PLCC84 socket, 1/2CAN TTL OSC socket with jumper option to wire it to the GCK1 input (pin 9). It also has the JTAG port connections and pads for all of the IO ports. Bypass cap. pads were also included.

I've built out one and installed the IC and verified that I could program it using the Xilinx ISE software. I found a "Parallel cable 3" compatible adapter from ebay for $10. (minor mod needed to get it working)

If anyone is interested in getting my pc board or info on the adapter, let me know.

Daryl

Am interested. I dont plan to build a seperate board, I am putting in the JTAG connector on this rev 2 board, but ti salways good to make sure I am doing it right for this design.

Cable I picked up from Diligent, JTAG3 cable, 20 bucks. Ah well, should have hit ebay first....

_________________
"My biggest dream in life? Building black plywood Habitrails"

I've uploaded a picture of the XC95108 board. Each board cost me $10.50. I have 4 available I'll sell for $10 each (including shipping).

Here is the link to the picture:
http://sbc.rictor.org/support/plcc.gif

Here is a link to adapter on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0028477623

The mod involves removing two resistors and crossing them over.
[added] You also have to add one resistor across the DB-25 connector pins

You can email me with questions.
daryl@rictor.org

Daryl