standalone atmega168 and serial communication


i'm building a device based on atmega168 and developed using arduino. it will communicate with a gsm module using rs232. i got some max3232 and i read resources about running the atmega168 standalone, and about interfacing it to a max3232.

when i found the page i got confused: there the use of some inverters and a DB9 connector for the serial communication is shown.

I thought: it can't be used for usb connection, because i would need the ftdi chip, and also because inverters have ttl levels (0-3.3V), but it doesn't match rs232 specific, too...

so, what's the benefit of this configuration?

thanks, athos

That standalone drawing is a very poor example (and with errors) of serial interfacing. Stick to your use of a max 2323 for proper interfacing to a RS-232 port..


yes, i will. but i was curious about that solution and where it could be useful. thanks!


but i was curious about that solution and where it could be useful

It's useful if you don't care if it will work with all serial ports you might come across, and you don't care about noise immunity and you don't care about potentially damaging the 7404 by putting negative voltages on the input. Other than that it's great. ;)

Actually, that "solution" isn't good for much of anything, since the RX inverter is backwards: it can talk, but it can't listen. Well, maybe it could be useful if you were going to have an Arduino as a guest on a cable TV news show...

Otherwise, about the only reason to use inverters would be if, say, you lived in the desert, the closest place you could buy a MAX232 was over 75 miles away, and you forgot to buy some the last time you mail-ordered in some parts. Works for me ;)


ok, i thought that there was something too smart for me to understand, in those inverters' choice.


thank you all, athos