Universal synchronous/asynchronous receiver transmitter (USART/UART) RM0440
1664/2126 RM0440 Rev 4
37.7.9 USART interrupt and status register [alternate] (USART_ISR)
Address offset: 0x1C
Reset value: 0x0X80 00C0
X = 2 if FIFO/Smartcard mode is enabled
X = 0 if FIFO is enabled and Smartcard mode is disabled
The same register can be used in FIFO mode enabled (this section) and FIFO mode
disabled (next section).
FIFO mode enabled
Bits 31:5 Reserved, must be kept at reset value.
Bit 4 TXFRQ: Transmit data flush request
When FIFO mode is disabled, writing ‘1’ to this bit sets the TXE flag. This enables to discard
the transmit data. This bit must be used only in Smartcard mode, when data have not been
sent due to errors (NACK) and the FE flag is active in the USART_ISR register. If the
USART does not support Smartcard mode, this bit is reserved and must be kept at reset
value.
When FIFO is enabled, TXFRQ bit is set to flush the whole FIFO. This sets the TXFE flag
(Transmit FIFO empty, bit 23 in the USART_ISR register). Flushing the Transmit FIFO is
supported in both UART and Smartcard modes.
Note: In FIFO mode, the TXFNF flag is reset during the flush request until TxFIFO is empty in
order to ensure that no data are written in the data register.
Bit 3 RXFRQ: Receive data flush request
Writing 1 to this bit empties the entire receive FIFO i.e. clears the bit RXFNE.
This enables to discard the received data without reading them, and avoid an overrun
condition.
Bit 2 MMRQ: Mute mode request
Writing 1 to this bit puts the USART in Mute mode and resets the RWU flag.
Bit 1 SBKRQ: Send break request
Writing 1 to this bit sets the SBKF flag and request to send a BREAK on the line, as soon as
the transmit machine is available.
Note: When the application needs to send the break character following all previously
inserted data, including the ones not yet transmitted, the software should wait for the
TXE flag assertion before setting the SBKRQ bit.
Bit 0 ABRRQ: Auto baud rate request
Writing 1 to this bit resets the ABRF flag in the USART_ISR and requests an automatic baud
rate measurement on the next received data frame.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and must
be kept at reset value. Refer to Section 37.4: USART implementation on page 1595.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. Res. Res. Res. TXFT RXFT TCBGT RXFF TXFE
RE
ACK
TE
ACK
WUF RWU SBKF CMF BUSY
rrrrrrrrrrrr
1514131211109876543210
ABRF ABRE UDR EOBF RTOF CTS CTSIF LBDF TXFNF TC RXFNE IDLE ORE NE FE PE
rrrrrrrrrrrrrrrr
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