Signalling voltage question

[Steve_Alaniz]

Originally Posted by Kevin Sevcik

Almost. But the MAX232 chips need a 5V supply and thus have 5V TTL outputs.

ONLY if you eliminate the capacitors that are suggested for the chip. They provide a "Charge Pump" that shifts the voltage levels from 0-5V to about -10v to +10v.. then it's just operating as a line driver...not it's main design function. ( Output... oh, you mean the TTL side of the chip. since you have an RX and TX on both sides, you really can't say one side is input and the other output. A little terminology cross talk there.) It's a really nice chip! Not that this really matters because ....

Originally Posted by Kevin Sevcik

I think you more likely want something along the lines of the MAX3232E which can operate from a 3.3V supply.

I agree... this would be the way to go. There are internal capacitors that do the voltage boost so you can use the TTL 0 -3.3V and get the RS232 on the output. Too bad you just can't bypass the OI RS232 shift and just go TTL to TTL.

Steve