RS232 to TTL (inverted, idle = 0v)

Help & Support Robot Parts
1

Hello all,

I need to convert an RS232 signal to TTL with an idle line level of 0v (rather than the default of 5v or 3.3v). This seems to be quiet hard to find. However, I’ve found two products which might fit my needs. They list a ‘tx inverted’ with a reference to the manual of the MAX3238 chip. That I find hard to understand.

My question: does this mean that with the products listed below that I can send via RS232 signal to a TTL device with a idle line of 0v?

Thanks in advance, Maarten

www.robotshop.com/eu/droids-db9-serial-adapter-5.html
www.robotshop.com/eu/pololu-serial-adapter-4.html

2

The idle line will be indeed 0 when converting RS232 signals to TTL with these converters. TTL in general would not support negative voltages such as the ~-7V of an RS232 idle line. Basically, the signal is shifted up so the idle is at 0V and chopped at 5V.