Three important reasons:TTL, RS232 and RS485 are the converters. UART is hardware module in microcontroller.
Can UART directly transmit and receive data without a converter? if it can't then why can't it ?
That's a pretty good generalisation. RS232 is going out of fashion because it needs ±12V power supplies, and because it is limited to one source and one destination. RS485 can have multiple transmitters and receivers, but you have to design the software so that only one can transmit at once.This means that if we have to send or receive data over long distances, then we should use RS485 converter. And at less than that distance RS232 should be used. And less than that distance TTL converter should be used.
The conclusion is that the selection of the converter depends on the transmission distance.
Only the physical RS-232 line circuit (RS-232 inputs/outputs) will have +- voltage, everything thing else will be at the logic level voltages (5V, 3.3V, etc ...) of the micro-controller, USB or laptop.Saves Board Space
Integrated Charge Pump Circuitry
Eliminates the Need for a Bipolar ±12V Supply
Enables Single Supply Operation from +5V Supply
Integrated Capacitors (MAX223, MAX233, MAX235, MAX245–MAX247)
Saves Power for Reduced Power Requirements
5µW Shutdown Mode
The microcontroller sends either 0V (for Logic 0) and 3.3V or 5V (for logic 1) (these are generally known as "TTL Levels") to the transceiver. If the input to the transceiver is 0V, the output on the RS232 line is +12V and if the input is 3.3V or 5V the output is -12V.What will be the voltage level between the microcontroller and the laptop when the microcontroller transfers a character to the laptop over usb to rs232 converter
I have downloaded this picture from internet please have a look at it. It uses only one trans receiver between two devicesAs others have said, when two devices are connected via RS-232 they need RS-232 transceivers at both ends of the cabling.
It doesn't show the other one that is in the USB to DB9 converter.I have downloaded this picture from internet please have a look at it. It uses only one trans receiver between two devices
View attachment 283999
Because one end of it connects to the USB port of the laptop, that's why I was thinking that it would also use the USB protocol.
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