Difference between revisions of "AVR serial communications"
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==Registers== | ==Registers== | ||
;Enabling USART functions: Set RXEN and TXEN in '''UCSRB''' (USART Control and Status Register B) to enable serial reception. | ;Enabling USART functions: Set RXEN and TXEN in '''UCSRB''' (USART Control and Status Register B) to enable serial reception. | ||
| − | ;Setting the baudrate: '''UBRR''' (USART Baud Rate Register) Sets the baud rate. The baud rate is f<sub>osc</sub>/(UBBR+1) '''divided''' by 2, 8 (U2X = 1) or 16 (U2X = 0). U2X is located in '''UCSRA'''. | + | ;Setting the baudrate: '''UBRR''' (USART Baud Rate Register) Sets the baud rate. The baud rate is f<sub>osc</sub>/(UBBR+1) '''divided''' by 2 (?), 8 (U2X = 1) or 16 (U2X = 0). U2X is located in '''UCSRA'''. UBRR is divided into two 8-bit registers ('''UBRRH''', '''UBRRL'''). |
;Choosing the frame format: UCSZ0 - UCSZ1 (in '''UCSRC'''), and UCSZ2 (in '''UCSRB''') can be used to set the number of databits (USART Character Size: 5, 6, 7, 8, ''reserved'', ''reserved'', ''reserved'',9) . UPM0 - UPM1 (USART Parity mode: none, ''reserved'', even, odd) and USBS (USART Stop Bit Select: one bit, two bit) are in '''UCSRC'''. Default is ''8n1''. '''Note''': on atmega16, al writes to UCSRC must have bit ''URSEL'' set, otherwise the write will redirect to the UBRRH register. | ;Choosing the frame format: UCSZ0 - UCSZ1 (in '''UCSRC'''), and UCSZ2 (in '''UCSRB''') can be used to set the number of databits (USART Character Size: 5, 6, 7, 8, ''reserved'', ''reserved'', ''reserved'',9) . UPM0 - UPM1 (USART Parity mode: none, ''reserved'', even, odd) and USBS (USART Stop Bit Select: one bit, two bit) are in '''UCSRC'''. Default is ''8n1''. '''Note''': on atmega16, al writes to UCSRC must have bit ''URSEL'' set, otherwise the write will redirect to the UBRRH register. | ||
| + | ;Receiving data (synchronously): Can be performed by waiting until RXC in '''UCSRA''' has been set and then reading the '''UDR''' register. Reading from UDR will clear RXC. | ||
| + | ;Sending data: can be performed by first checking bit UDRE in '''UCSRA''' and then writing to '''UDR'''. | ||
| + | ;Interrupt driven reception: This can be achieved by implementing the ISR for USART (''USART_RXC_vect''), enabling the RXC interrupt by setting RXCIE in '''USCRB''' and allowing interrupts globally, by using the '''''sei()'''''-macro. | ||
Latest revision as of 22:07, 12 July 2010
Notes on getting serial communications to work on AVR.
Registers
- Enabling USART functions
- Set RXEN and TXEN in UCSRB (USART Control and Status Register B) to enable serial reception.
- Setting the baudrate
- UBRR (USART Baud Rate Register) Sets the baud rate. The baud rate is fosc/(UBBR+1) divided by 2 (?), 8 (U2X = 1) or 16 (U2X = 0). U2X is located in UCSRA. UBRR is divided into two 8-bit registers (UBRRH, UBRRL).
- Choosing the frame format
- UCSZ0 - UCSZ1 (in UCSRC), and UCSZ2 (in UCSRB) can be used to set the number of databits (USART Character Size: 5, 6, 7, 8, reserved, reserved, reserved,9) . UPM0 - UPM1 (USART Parity mode: none, reserved, even, odd) and USBS (USART Stop Bit Select: one bit, two bit) are in UCSRC. Default is 8n1. Note: on atmega16, al writes to UCSRC must have bit URSEL set, otherwise the write will redirect to the UBRRH register.
- Receiving data (synchronously)
- Can be performed by waiting until RXC in UCSRA has been set and then reading the UDR register. Reading from UDR will clear RXC.
- Sending data
- can be performed by first checking bit UDRE in UCSRA and then writing to UDR.
- Interrupt driven reception
- This can be achieved by implementing the ISR for USART (USART_RXC_vect), enabling the RXC interrupt by setting RXCIE in USCRB and allowing interrupts globally, by using the sei()-macro.