Rs 232 transceiver

Hi,

I have a very basic doubt.
Wherever I see RS-232 circuits online and in people's designs they use RS-232 transceivers when connecting a processor and a RS 232 device.

But when we connect our arduino I have not seen people use such a transceiver. What is the reason for that?

RS232 signal voltages are not compatible with the Arduino's TTL signal voltages so you need something like a MAX232 to convert between the two.

...R

If I understand your question correctly, the reason there's no RS232 device on your Arduino, is that it uses a USB to TTL serial transceiver instead.

Years ago, before USB was invented, devices communicated over a "real" serial port and we had to have RS-232 transceivers to drive the serial data over several 10's of feet of cable to the other device which also had an RS-232 transceiver.

Thank you Robin2 and markd833.

markd833:
If I understand your question correctly, the reason there's no RS232 device on your Arduino, is that it uses a USB to TTL serial transceiver instead.

Years ago, before USB was invented, devices communicated over a "real" serial port and we had to have RS-232 transceivers to drive the serial data over several 10's of feet of cable to the other device which also had an RS-232 transceiver.

No I do not mean to refer to the USB to serial connection.
I meant to ask about the Pin 0 and Pin 1, which we can directly connect to a device with UART interface. Suppose I get a GPS device which gives RS-232 output. If I connect it to Pin 0 and Pin 1, then it is directly connected to my atmega chip, right? I am not using the USB to TTL IC in this case

I assume you are referring to TTL RS232 which uses 0-5v signalling levels. You can connect the Arduino Tx pin on the header direct to the Rx pin on your other module. However, you need to be careful connecting to the Rx pin on the header. Another device (usually the USB to serial converter IC) is driving this pin.

If you connect directly to this pin, then you will have an issue when the USB interface is driving the pin high and your other board is trying to drive the pin low.

markd833:
I assume you are referring to TTL RS232 which uses 0-5v signalling levels. You can connect the Arduino Tx pin on the header direct to the Rx pin on your other module. However, you need to be careful connecting to the Rx pin on the header. Another device (usually the USB to serial converter IC) is driving this pin.

If you connect directly to this pin, then you will have an issue when the USB interface is driving the pin high and your other board is trying to drive the pin low.

I think this answers my question. Probably the devices I saw directly connected to arduino on UART port were using TTL RS232

markd833:
I assume you are referring to TTL RS232

The phrase "TTL RS232" is wrong.

You can have TTL serial or RS232 serial but not TTL RS232. TTL defines one set of voltage levels and RS232 defines a different set of voltage levels.

...R

Oops, my mistake. Robin is correct.