Difference between revisions of "AVR serial communications"

Revision as of 01:01, 3 December 2009

Notes on getting serial communications to work on AVR.

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_osc/(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.

@@ Line 6: / Line 6: @@
 ;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.