hoglet

Use of D53 (INIT_B) as an input

4 posts in this topic

I'm using the 16 bit input wing (LXC16245 based) and, for physical reasons, I would like to plug this into ports DH/DL on the Duo.

When I do this, I'm sometimes experiencing a failure for the design to configure, until the wing is physically removed.

I've tracked this down to pin Bit 0 of the wing being low. This connects to D53 which is then routed to the Xilinx INIT_B pin.

So it seems like D53 cannot safely be used as a user input (both the shields use this as an output so are fine).

Is this a known issue?

I can work around this by simply not using Bit 0 of the input wing, and tying it high. But I'm concerned of the possibility of conflicts during configuration, as INIT_B is an open drain output, and can this be driven low.

I guess I could go one step further and de solder the pin on the wing that connects to the Duo.

Anyone got any thoughts on this?

Dave

Share this post


Link to post
Share on other sites

Hello Dave,

I was trying to squeeze every pin possible into the DUO design to fill the Arduino Mega footprint. INIT_B has a pullup resistor on it so it will be at 1 during bootup and everything can proceed, but unfortunately it does mean that any input that pulls it down to 0 at bootup will hang up the FPGA...

Sorry that was not documented, I'm putting it on my task list to update the documentation for this gotcha.

Jack.

Share this post


Link to post
Share on other sites

Thanks for confirming this Jack.

In the end I just de-soldered bit 0 of the wing, and reconnected the signal elsewhere.

It's now working fine.

Dave

 

Share this post


Link to post
Share on other sites

Good, glad to hear you have a solution, sorry for the inconvenience.

Jack.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now