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By roach
#10231
Another newbie question: I (kind of) know what rs232 is (or at least, I've heard of it). What is the TTL serial I read about all over the place?

Which of these two is used by the atmega128 USART0 and USART1?

Thanks for your patience...
By transcendentnb2
#10232
RS232 is a standard for serial communication. It uses usually a +-13v signal with a common ground. Usually a PC or any other device uses an RS232 converter chip to change the TTL or CMOS signals (5v or about 3v) into the required levels for RS232. On the other end, another RS232 chip would convert the +-13v signal back down to TTL or CMOS level. Your serial cable on your computer will most likely be RS232.


Microcontroller1 <----- TTL Signal -----> RS232 Chip1 <----- +-13v Signal (external DB9 Serial cable) -----> RS232 Chip2 <----- TTL Signal -----> Microcontroller2

As I already hinted above, TTL serial is simply a 0v or +5v signal. Many people use TTL serial to communicate between closely positioned devices (common in embedded systems). Every microcontroller that I've used outputs at TTL levels for its serial connection and relies on the user to decide if they want to keep the TTL levels or convert it to RS232 by means of an external chip. Having an RS232 converter built into a chip is useful in that it requires less external hardware, but I haven't personally seen this as being common.

The ATmega's use "TTL". Development boards will usually come with a built in RS232 converter so you can communicate with your PC.
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By roach
#10235
sweet! Thanks for the response, tran. So, if I understand correctly. When interfacing my atmega128 with one of Sparkfun's USB or Bluetooth USART modules, I can just wire RX -> (both ways), write some code to handle the data, and presto!

...or is this over-simplifying. I haven't been at this long, but this seems like the first "simple" thing I've come across:)
By transcendentnb2
#10236
Well, doing all that isn't as easy as "presto!", heh. But yes, you can directly connect them.

HOWEVER, be careful on if the modules are using 5V or 3V levels!!! From what I've seen, the bluetooth modules are 3v signals.

SparkFun provides the necessary info in their schematics for converting if necessary. You probably won't kill anything, but be careful.