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UART to RS232 or USB adapters PDF Print E-mail
Written by Bojan Kovač   

The abbreviation UART stands for Uni­ver­sal Asynchronous Re­ce­i­ver/Tran­smit­ter. It is a serial data interface with a defined speed. Regardless of the actual voltage level of the RS232 signals, these RS232/RS482 devices present signals to the microcontroller as a logical 0 or 1.

This protocol sends data to the microcontroller serially, which means the data stream must be converted back to parallel (which is the function of the UART block in the microcontroller). A block diagram of such a data transfer is shown in Figure 1.

Data transfer via the USB bus is similar to RS232 with a some differences: USB is a faster transfer method, and to interface it with a microcontroller, we can use a USB to UART bridge, such as the FT232RL made by Future Technology Devices International LTD (FTDI) [1].

There are a variety of different asynchronous serial adapters available on the market. Bascom-AVR communicates with all of these with one statement meant to send data to the AVR’s UART- the Print statement.

Probably there is no other microcontroller language with as simple a statement to control the UART, as Bascom/AVR. There are numerous UART parameters that must be configured, but many of them are changed very infrequently, so we can often just use the default settings.

When designing a new device, I always reserve pins for serial communications. That allows me to easily change program parameters, not to mention being able to externally store data from the microcontroller.

Logic levels amongst digital devices vary. Usually a logical 1 is either 5.0 V or 3.3 V (and more recently,1.8 Volts). Generally the logic levels depend upon the microcontroller’s power supply voltage rating. This can present a problem, as not all microcontrollers and peripheral devices work at the same voltage. So, for example, a simple connection between your mobile phone and a USB or RS232 port may be problematic. The solution to this is to use level-shifting devices (usually ICs) that present suitable logic levels to both sides of the communications link.

For serial communications we use two signals: Rx and Tx, both of which are referenced to GND.

UART to RS232 or USB adapters


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Last Updated on Wednesday, 01 August 2012 14:46
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