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Discussion Groups | FPGA-CPU | Re: Re: TTL computing

This list is for discussion of the design and implementation of field-programmable gate array based processors and integrated systems. It is also for discussion and community support of the XSOC Project (see http://www.fpgacpu.org/xsoc).

Re: TTL computing - Ben Franchuk - Apr 14 10:00:00 2002

Richard Erlacher wrote:

> If you buy a moderately cheap CPLD, e.g. the XILINX 95108, in a PLCC84, it
> costs about $20-30 U.S. at DigiKey. Combine that with a socket, ($4 tops) and
> a few wirewrap socket pins, ($.10 each) that's another $8.40. Now find a
> cheap wirewrap board to which you can solder ... and then use the free
> software and build the ~$5 ISP adapter.
Has anybody done that?

> For the same money, you can use a
> Xilinx SPARTAN-series FPGA which you can also program using the ISP
> programmer, though you'll have to do it every time. Then you can design
> pretty much whatever small computer (only because of pin-count limitations)
> you want. These devices even allow you to put in some RAM.
>
I have a nice FPGA prototype kit, (altera) but I am having problems
getting A PROM for it. I may go to using smaller chips like the XC-9572
(72 macro cells) ? $12 canadian. They don't make wire wrap PLCC sockets
(or not in DigiKey) so I will end up with making a PCB. I have a new CPU
design and expect about 10 CPLD's in total.
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html


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Re: Re: TTL computing - Philip Freidin - Apr 14 13:49:00 2002

On Sun, 14 Apr 2002 09:00:50 -0600, Ben wrote:
>I have a nice FPGA prototype kit, (altera) but I am having problems
>getting A PROM for it. I may go to using smaller chips like the XC-9572
>(72 macro cells) ? $12 canadian. They don't make wire wrap PLCC sockets
>(or not in DigiKey) so I will end up with making a PCB. I have a new CPU
>design and expect about 10 CPLD's in total.

Before you give up on wire-wrap, PLCC sockets (through hole, not surface
mount sockets) have their pins on a .1 inch grid. I have often used strips
of N x 1 wirewrap socket pins, cut to length, and made up ww sockets to
match the underside of a PLCC socket. Such as these:

http://www.mill-max.com/images/products/PDF/049.pdf =================
Philip Freidin



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RE: Re: TTL computing - Aare Tali - Apr 14 14:21:00 2002

> > If you buy a moderately cheap CPLD, e.g. the XILINX 95108, in a
> PLCC84, it
> > costs about $20-30 U.S. at DigiKey. Combine that with a

$28.65 for single fastest 7ns CPLD, $12.10 for single slowest CPLD, $3.50
for XC9572-PLCC84 on ebay.

> socket, ($4 tops) and
> > a few wirewrap socket pins, ($.10 each) that's another $8.40.

If you are 'breadboard' type, you can buy regular through-hole socket and
when soldering it on the board put usual 0.1" pin strips into holes and
solder them both in same hole. So you get reasonably cheap socket and wire
wrap pins at same time. Doesn't look nice, but the mess is on solder side
that is usually the bottom.

> Now find a
> > cheap wirewrap board to which you can solder ... and then use the free
> > software and build the ~$5 ISP adapter.
> Has anybody done that?

I made cable using drawing at
http://www.xilinx.com/support/programr/jtag_cable.pdf, works fine for both
5V and 3.3V supply (74HC125).

> > For the same money, you can use a
> > Xilinx SPARTAN-series FPGA which you can also program using the ISP
> > programmer, though you'll have to do it every time. Then you can design
> > pretty much whatever small computer (only because of pin-count
> limitations)
> > you want. These devices even allow you to put in some RAM.
> >
> I have a nice FPGA prototype kit, (altera) but I am having problems
> getting A PROM for it. I may go to using smaller chips like the XC-9572
> (72 macro cells) ? $12 canadian. They don't make wire wrap PLCC sockets
> (or not in DigiKey) so I will end up with making a PCB. I have a new CPU
> design and expect about 10 CPLD's in total.

Spartan-2E board from nu horizons ($99) is probably cheaper and faster to
buy than making your own, with FPGA or 10+ CPLDs. Reasonably big FPGA, but
board could be better if they used XC2S200 without E for 5V I/O or XC2S300E
for bigger FPGA. Now I just have to breadboard some RAMs (using wire wrap
sockets described above) and go play with it.




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Re: Re: TTL computing - Ben Franchuk - Apr 14 15:36:00 2002

Aare Tali wrote:
> $28.65 for single fastest 7ns CPLD, $12.10 for single slowest CPLD, $3.50
> for XC9572-PLCC84 on ebay.
I have never had luck with ebay.

> Spartan-2E board from nu horizons ($99) is probably cheaper and faster to
> buy than making your own, with FPGA or 10+ CPLDs. Reasonably big FPGA, but
> board could be better if they used XC2S200 without E for 5V I/O or XC2S300E
> for bigger FPGA. Now I just have to breadboard some RAMs (using wire wrap
> sockets described above) and go play with it.

I still need a X-brand prom burner and prom . :(
Btw I think I will need about 4 or 6 CPLD'S for the data path and 3 more
for the control logic.
The CPLD's look to be cheaper than ONE big FPGA and PROM.
Since I plan on using a 4x clock @ 4.1952 Mhz that will give me a 800 ns
memory cycle and close to REAL PDP-8 speeds for a 24 bit computer. Rough
calculations give me 12-14 levels of gating , thus at say 20 ns delay (
LS - speeds ) I will have a cycle time of around 280 ns. Lets not forget
one needs a lot of I/O pins for a hardware front panel - switches and
lights. Until I get the software downloaded ( cross fingers ) and things
mapped out I will not know for sure.

Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html


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Re: Re: TTL computing - Ed Corter - Apr 14 20:01:00 2002



This may sound crazy.. but so am I..

I recently built, by hand, my own FPGA developement board. I mounted a Xilinx Virtex 300BG352 upside down on standatd plated through-hole prototype board ( bread borad ) and used 30 gauge kynar insulated wire with a color scheme to make assembly easy. seperating ground, IOvcc, core vcc and IO pins. On the reverse side of the board I created three 20 gauge square'rings' for the two powers and ground and there I placed all off the requred bypassing capacitors.
the two required power supplies( 2.5v and 3.3v ) were easily built from a national semiconductor app note using 500 khz switchers that were sampled to me .. all other parts except the shottky diodes were purchased at radio shack.
the Jtag port and the user IO was brought out to standard .1 spaced headers.
I hand soldered the 30 guage from the bga to the headers and used super glue for wire strain relief as I progressed. The whole effort took less than 20 hours and cost less than 100 bucks !!
I recently put the board to a real test and was pleased with the results.
I used a 2x dll configuration to sample data at 54 mhz as a logic analyser , using some registers and and xilinx ILA instantiated.
if anyone else is crazy and has good soldering skills and wants to construct a board like mine feel free to send me questions at ps the board is still working !!! Ed
---------------------------------




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