wtb: spartan2 board, 5v tolerant

[legacy]

hi
I am going to interface an old 32bit/5V bus.

I know I could use a big XC95108(or 144?)/XL cpld, but I need more resources and a lot of bram. I could use a modern spartan6, but it would probably end with the use of a lot of voltage-level translator chips, something like four chips for the address line, four chips for the data bus, and probably other two chips for the the control lines.

I am not a guru at pcb-designing, thus I'd prefer to keep the design the simplest.

Thus I am looking for a spartan2 board, something simple with just the fpga chip, eventually the configuration flash chip, but I really need is fpga's pins exported on a couple of comfortable connectors.


Let me know if you have something for sale.

Thanks.

[radar_macgyver]

If the speed is low enough, you could use some series resistors for the address bus (since it is unidirectional) and add bus switches just for the data bus and control lines. Even those could be done using a SN74CBT34X245, 32 bus switches in an 80-pin TSSOP, for $3 on Digi-key. How well this works would be a function of the bus speed (I'd estimate it all falls apart at maybe 20 MHz or so).

[edpalmer42]

Would a Spartan 3 be acceptable?  I was looking at this board for a project that never happened.  Includes 30 5V-tolerant GPIO pins.

https://www.micro-nova.com/mercury/

[legacy]

If the speed is low enough

eh, the BUS clock is 12.5Mhz, it's definitively "fast" enough.

[legacy]

Would a Spartan 3 be acceptable?

Well, Spartan 3 is NOT 5V tolerant. Maybe there are boards around with some trick like a bunch of voltage level translator chips already soldered.

[legacy]

Yup, look at the picture, down on the right, it's written "level shifting". So the board uses the trick

Flexible I/O
Most FPGA development boards are limited to 3.3V digital-only I/O, but we built Mercury with more flexibility in mind: We've included an onboard 8-channel SPI ADC (10 bit, 200 Ksps), great for interfacing with sensors or for audio input. It also has 30 pins of 5V-tolerant digital I/O, so you can safely interface TTL-level devices with the 3.3V Spartan-3A FPGA.