rs232 and usart

[srdp45]

hi, what's the difference between USART and RS232 ??
both is for pc serial communication only, then why only USART for pc serial communication in pic16f877a microcontroller is recommended and why not RS232 ??

[waltr]

RS232 signals are +12V to -12V and are only needed for longer cable lengths. This is the voltage levels on a PC's Serial COMM port and has been an industrial standard for over 40 years and allows easy interfacing to many different devices with high reliability.

The PIC's UART (and other processors) are power at 5V or 3.3V so can not supply the RS232 voltage levels.

The data timing is the same on both, a logic to RS232 level translator like a MAX232 chip only changes the voltage.

Look up both RS232 and Asynchronous Serial in Wikipedia for details.

[MikeK]

USART is the device.  RS232 is the communications standard, which wasn't always strictly adhered to anyway.  And hardly is anymore.  Old PCs that used the RS232 standard still had a dedicated UART chip on-board.