Datasheet

221
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
19.7 USART MSPIM Register Description
The following section describes the registers used for SPI operation using the USART.
19.7.1 USART MSPIM I/O Data Register - UDRn
The function and bit description of the USART data register (UDRn) in MSPI mode is identical to normal USART
operation. See “USART I/O Data Register n– UDRn” on page 209.
19.7.2 USART MSPIM Control and Status Register n A - UCSRnA
• Bit 7 - RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty
(i.e., does not contain any unread data). If the Receiver is disabled, the receive buffer will be flushed and
consequently the RXCn bit will become zero. The RXCn Flag can be used to generate a Receive Complete
interrupt (see description of the RXCIEn bit).
• Bit 6 - TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and there are no
new data currently present in the transmit buffer (UDRn). The TXCn Flag bit is automatically cleared when a
transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location. The TXCn Flag
can generate a Transmit Complete interrupt (see description of the TXCIEn bit).
• Bit 5 - UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is one, the
buffer is empty, and therefore ready to be written. The UDREn Flag can generate a Data Register Empty
interrupt (see description of the UDRIE bit). UDREn is set after a reset to indicate that the Transmitter is ready.
• Bit 4:0 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits
must be written to zero when UCSRnA is written.
Bit 7 6 5 4 3 2 1 0
RXCn TXCn UDREn - - - - - UCSRnA
Read/Write R/W R/W R/W R R R R R
Initial Value 0 0 0 0 0 1 1 0