Microchip Technology megaAVR 0 Series Manual page 307

22.5.7 Control B
Name: CTRLB
Offset: 0x06
Reset: 0x00
Property: -
Bit 7
RXEN
Access R/W
Reset 0
Bit 7 – RXEN Receiver Enable
Writing this bit to '1' enables the USART receiver. The receiver will override normal port operation for the
RxD pin when enabled. Disabling the receiver will flush the receive buffer invalidating the FERR,
BUFOVF, and PERR flags. In GENAUTO and LINAUTO mode, disabling the receiver will reset the auto-
baud detection logic.
Bit 6 – TXEN Transmitter Enable
Writing this bit to '1' enables the USART transmitter. The transmitter will override normal port operation
for the TxD pin when enabled. Disabling the transmitter (writing TXEN to zero) will not become effective
until ongoing and pending transmissions are completed (i.e. when the Transmit Shift register and
Transmit Buffer register does not contain data to be transmitted). When the transmitter is disabled, it will
no longer override the TxDn pin, and the pin direction is set as input automatically by hardware, even if it
was configured as output by the user.
Bit 4 – SFDEN Start Frame Detection Enable
Writing this bit to '1' enables the USART Start Frame Detection mode. The Start Frame detector is able to
wake up the system from Idle or Standby Sleep modes when a high (IDLE) to low (START) transition is
detected on the RxD line.
Bit 3 – ODME Open Drain Mode Enable
Writing this bit to '1' makes the TxD pin to have open-drain functionality. A pull-up resistor is needed to
prevent the line from floating when a logic one is output to the TxD pin.
Bits 2:1 – RXMODE[1:0] Receiver Mode
In CLK2X mode, the divisor of the baud rate divider will be reduced from 16 to 8 effectively doubling the
transfer rate for asynchronous communication modes. For synchronous operation, the CLK2X mode has
no effect and RXMODE should always be written to zero. RXMODE must be zero when the USART
Communication mode is configured to IRCOM. Setting RXMODE to GENAUTO enables generic auto-
baud where the SYNC character is valid when eight low and high bits have been registered. In this mode,
any SYNC character that gives a valid BAUD rate will be accepted. In LINAUTO mode the SYNC
character is constrained and found valid if every two bits falls within 32 ±6 baud samples of the internal
baud rate and match data value 0x55. The GENAUTO and LINAUTO mode is only supported for USART
operated in Asynchronous Slave mode.
Value Name
0x0 NORMAL
0x1 CLK2X
©
2018 Microchip Technology Inc.
Universal Synchronous and Asynchronous Recei...
6 5
TXEN
R/W
0
Description
Normal USART mode, Standard Transmission Speed
Normal USART mode, Double Transmission Speed
4 3
SFDEN ODME
R/W R/W
0 0
Datasheet Preliminary
®
megaAVR 0-Series
2 1
RXMODE[1:0]
R/W R/W
0 0
DS40002015A-page 307
0
MPCM
R/W
0