I read in the datasheet for the ATF1504 (and 08) that it's I/O pins are 3.3V or 5.0V compatible. However, I don't think this applies to the 44 pin versions as I don't see VCCIO pins.

Is my assumption correct? Is there a way to use 3.3V I/O without level shifters?

Thanks

_________________
Cat; the other white meat.

Looking at the datasheet it appears you will have to use level shifters, is your whole system running at 3v? if so you might want a different CPLD like the EPM7064A (5V I/O capable if you need to do both) or XC9572 bonus is that you can then use VHDL/Verilog/Schematic capture

The CPLD will run on 5V but the rest of the system is 3.3V, is that what you mean?

I'm guessing any of this CPLD's pins that's used as an output won't exceed 3.3V anyway, so that part is alright. And, as inputs, the CPLD pins probably respond to TTL voltage levels. That means they'll also accept the output of a CMOS gate running on 3.3V. Seems to me you should be good to go, without any level shifters required (but I haven't read the datasheet).

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Yes, my system is 3.3V for the most part. I'm in the prototyping (wire-wrapping) stage now. Unfortunately, I'm stuck with the parts that I already have. Such as a ATF1508 and ATF1504. Plus, a couple TinyFPGA's.

The ATF1508 has several VCCIO pins with, IIRC, accept the voltage for the I/O pins. Meaning that if I put 3.3V on VCCIO, the the I/O pins will accept 5V inputs (or 3.3V) but only output 3.3V to other devices.

I'll do some more research. Fortunately, the need I have is mostly input on the CPLD (MMU) so maybe I could use some resistors for the few outputs on it.

Thanks.

_________________
Cat; the other white meat.

OK, the CPLD pins which are inputs are clearly gonna be alright.

As for outputs, that question supposedly depends on the vccio pin (which you lack, and can't connect to 3V). So, the chip is gonna supply what it considers to be 5V outputs. But they won't really go to 5V, and I'd be tempted to just connect 'em straight to the surrounding 3V circuitry. That's me, though. Other folk might be more cautious.

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Yeah, I think you are correct. This is for prototyping anyway. Most of the components, even though they are 3v3, are 5v tolerant (like my SRAM). I was just trying to do it the "right" way.

Final design will be different anyway.

Thanks for the input!

_________________
Cat; the other white meat.