ADSP-21469 has one UART, and I need two.
Is it easy to add an extra external UART? What could I use?
You should look into using a SPORT either all by itself or with the help of some programmable logic.
Transmission is easy. Just set up the correct baud rate and number of bits. Make sure to include the stop bit so you end on a high bit.
The receive would require you to trigger an interrupt on the falling edge of the start bit. This would then start a delay for half a bit time before you start the receive operation.
Obviously you would need to add a bit of software to check for framing or parity errors.
Using programmable logic would allow you to detect the start bit externally and generate the receive clock to turn the incoming data into a clock synchronous stream. A flexible way of doing this would be to provide a clock that is a multiple of your baud rate to the programmable logic, so it can oversample the incoming data to center the generated SPORT clock relative to the receive data.
There are also chips available that function as a bridge between I2C / SPI and UART.
NXP, Maxim and Exar all have parts like this.
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