Unused RS232 Pins

Penn Linder

Other Parts Discussed in Thread: MAX232E, TRS232

Should unused RIN pins on devices such as the MAX232E and TRS232 be tied to a voltage level (like ground) if not used? What about RIN pins that will be driven when a cable is connected, but will not be driven when a cable is disconnected?

over 15 years ago

0 Ron Michallick over 15 years ago

TI__Guru**** 169476 points

Hello Ivek Engineer,

The unused RIN inputs can be left unconnected. They have internal resistors (~5k ohm) to ground. The ROUT will be high with no input source.

Grounding the RIN inputs is also acceptable.

Regards,
Ron M.

0 Brad A over 14 years ago in reply to Ron Michallick

Prodigy 50 points

What about the TIN inputs? This is in reference to the MAX232N. I can see no reference to whether it has pullups (downs) on the TTL side inputs.

Thanks,

Brad A.

0 Ron Michallick over 14 years ago in reply to Brad A

TI__Guru**** 169476 points

Hello Brad,

Unused DIN pins should be tied either to ground or VCC.
There are no pull up/down resistors [mentioned in the data sheet, however they do exist].
[The "short-circuit input current spec specifies the maximum current]

Regards,
Ron Michallick

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Unused RS232 Pins