MOD5234 gpio voltage tolerance

[thomastaranowski]

I've got a device that outputs a 5v signal. Can I just wire that signal up to one of the 5234 gpio pins, or is that bad? I couldn't find where the voltage tolerances for the gpio pins was documented. Anyone know where to find that info?

Thanks!

[Ridgeglider]

That would be bad... 3.3V limit! See the bottom of this page: http://www.netburner.com/products/core_ ... d5234.html

[v8dave]

Hi there,

Depening on the type of output and speed of the signal, you can interface this a number of ways to the GPIO pins.

The first is a simple transistor with a pull up on the collector to 3.3V. Apply the 5V signal to the base via a 4K7 resistor (actual value will depend on the current available from your 5V output) and then you will be able to read the inverted version of your 5V output.

Another option is to use one of the many voltage level convertors from the likes of Analog Devices or Maxim. I like the AD devices as they are available up to 1MB so ideal for SPI etc. They also do one for I2C. I use them with an isolated ADC circuit and they work just great.

Dave...

[thomastaranowski]

Thanks v8, that was helpful. The ADG33xx series looks pretty nice, and easy to use For the translation I was thinking about going for a 74LVC.

I also found the following appnote helpful, although the resistors for the passive voltage divider approach they specify don't appear to be correct, as it output ~1.2v for me.
http://focus.ti.com/lit/an/swra071/swra071.pdf

I think I might bypass this whole issue by feeding into a fifo, and use 3.3v for Vcc on my fifo, and use that to do my ghetto logic level translation.

[v8dave]

Can I ask what the device is that you are using?

Can it be powered from 3.3V instead?

Dave...

[thomastaranowski]

Unfortunately not, as the data sheet specifies +5v. It's this device here: http://www.idquantique.com/images/stori ... ppnote.pdf .

[fanat9]

Looks like it have 3.3V outputs: "The QUANTIS module must be powered by 5V, although it internally uses 3.3V" and in GENERAL SPECIFICATIONS section: "Input and output LVTTL max. 3.3V"

[thomastaranowski]

Fanat,

Thanks for the reply. I thought it was 3.3v as well on this strobe line, but when I scoped it to verify it showed 5v peak to peak. ill check the other pins to see if they are at 3.3, or 5.

[v8dave]

Good that it is 3.3V as the data rate is 4Mbit/s which means fast edges and the potential dividor ideal would not be ideal there and possibly the transistor idea too.

Be interested to see how you get on with this and how is pans out.! Keep us posted?

Dave...