![]() By the RS-232 standard a logic high ('1') is represented by a negative voltage – anywhere from -3 to -25V – while a logic low ('0') transmits a positive voltage that can be anywhere from +3 to +25V. The two differ solely at a hardware level. RS-232 signals are similar to your microcontroller's serial signals in that they transmit one bit at a time, at a specific baud rate, with or without parity and/or stop bits. The serial port on your computer (if it's lucky enough to have one, they're quickly becoming a relic) complies with the RS-232 ( Recommended Standard 232) telecommunications standard. A logic high ('1') is represented by Vcc, while a logic low ('0') is 0V. Serial communication at a TTL level will always remain between the limits of 0V and Vcc, which is often 5V or 3.3V. ![]() ![]() This method of serial communication is sometimes referred to as TTL serial (transistor-transistor logic). UARTs transmit one bit at a time at a specified data rate (i.e. Most microcontrollers these days have built in UARTs (universally asynchronous receiver/transmitter) that can be used to receive and transmit data serially. These two devices are compatible from a software perspective, however you can't just hook a microcontroller up to a computer because the hardware interfaces are not compatible. Serial is very easy to implement, and it allows you to send/receive any data you need from your microcontroller to a computer's serial port so it can be viewed using a terminal emulator. One of the tools we use most when debugging our projects is serial input/output.
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