after supplying the max232 with Vcc(5v)(before connecting it to the circuit) i noted something strange


pins #10 and #11 are input pins but when measuring the voltage on them the multimeter reads 5v(without connecting them to any nodes)!!!

it's supposed to be 0 because i want to input TTL signal and max232 invert it to Rs232 level.

Note: i tried two different max232 ic's but the two have the same problem?

What's wrong with the IC?

Thank you

 

As long as the pins present a high impedance to the external signal, their no-load voltage is really irrelevant. The internal chip circuitry must be pulling the pins high, but it's the impedance of the pins as compared to the impedance of the driving signal that matters.

As long as the input signal is a low enough impedance, it will force the pins to the proper voltage in the circuit, regardless of the pins no-load voltage.

 

thanx davebee for the explanation