what to do with unused pins on MAX232/MAX233

[Michael Noone]

Hi - I'm just wondering - I'm working on a board that uses a MAX233 (it's a
MAX232 with internal caps). It has two RS-232 inputs and two RS-232
outputs. I'm only using one of each. What should I do with the ones that
I'm not using? In the back of my head something is telling me I should
ground the inputs (so RS-232 input input, and the RS-232 output input, if
you follow my wording). Is that right? Thanks!

-Michael J. Noone

 

[Rich Webb]

Hi - I'm just wondering - I'm working on a board that uses a MAX233 (it's a
MAX232 with internal caps). It has two RS-232 inputs and two RS-232
outputs. I'm only using one of each. What should I do with the ones that
I'm not using? In the back of my head something is telling me I should
ground the inputs (so RS-232 input input, and the RS-232 output input, if
you follow my wording). Is that right? Thanks!

It's always a good rule of thumb to tie unused inputs. However, the
MAX233 has built in pull-ups and -downs (400K up for TTL inputs and 5K
to ground on the RS-232 side) so in this case you're covered.