Hello everyone, I've been trying to make full grasp of what to do with unused outputs and/or inputs in CMOS and TTL.

I'm using FTDI's FT230XS chip (link below)

(http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT230X.pdf)

, and not making use of the RESET#, CTS#/RTS# or any of the CBUSx pins, and trying to be sure of what I can leave unterminated (the datasheet only states RESET# can be left unconnected).

It is my understanding CMOS outputs can be left unterminated and that TTL inputs need pull ups/downs. Now, from the datasheet I gather the chip already has internal pull-ups to VCCIO for the inputs. The outputs, being CMOS, don't require any pulling.

Is this correct?

Thank you a lot!

 

In general:

CMOS inputs must be terminated (except in the rare instance that they are internally terminated).

TTL inputs generally don't need to be terminated (they go high when un-terminated) but its good practice to do so to avoid any false triggering from noise.

Neither CMOS or TTL outputs need to be terminated.

 

All the unused input pins need to set to Low or Hi.

If All the unused input pins already settle down, and if any output pin is unused, you can left them behind, just don't care about them.

 

Yes as Scott say. Connect them to something ALWAYS. Either high or low. For Cmos I would have used a 4.7-10Kohm resistor. If you have time you can read this as a crash course
http://www.ti.com/lit/an/sdya009c/sdya009c.pdf

 

Leave all unused outputs alone.
All inputs have internal 75kΩ pullups. Unused inputs can be left alone.

 

Thanks to everyone.

 

Yes as Scott say. Connect them to something ALWAYS. Either high or low. For Cmos I would have used a 4.7-10Kohm resistor. If you have time you can read this as a crash course
http://www.ti.com/lit/an/sdya009c/sdya009c.pdf

As you mentioned that the values of the resistors, they can be using in everywhere, sometimes if the power comsumption is considered when the device is using at home or a portable, then the values can be raising to 47K~100K, but if using in the industrial that is better not to this, just using the values as you mentioned.