Signal loading by unpowered IC

Thread Starter


Joined Oct 19, 2010
I have some UART signals of 3.3V level , TX,RX ,CTS ,RTS.
Now I need to connect them to two devices one a normal RS232 driver other a UART to USB chipset.
The problem is The MAX232 driver and the UART to USB chipset bot function from different power inputs. So there will be times when one of the chipset would be unpowered .
I believe simutaniously connecting to both the drivers may result in loading from an unpowered chip if no power is applied.
How to get around the problem. As of now I am choosing Logic Multiplexer (74HC157) and ensuring the signals driving the unpowered chipset is 0V.

am i having the correct solution???.
Since it is a standart problem whats the way around....
Pls help