
UART
S3FB42F
16-4
UART STATUS REGISTER
The UART status register, USSR, is a read-only register that is used to monitor the status of serial I/O operations in
the single-channel UART.
Register
Address
R/W
Description
Reset Value
USSR
0xB2
R
UART status register
c0h
[0]
Overrun error
USSR[0] is automatically set to 1 whenever an overrun error occurs
during a serial data receive operation. If the receive status interrupt
enable bit, UCON[2] is 1, a receive status interrupt will be generated if
an overrun error occurs. This bit is automatically cleared to 0 whenever
the UART status register (USSR) is read.
[1]
Parity error
USSR[1] is automatically set to 1 whenever a parity error occurs during
a serial data receive operation. If the receive status interrupt enable bit,
UCON[2] is 1, a receive status interrupt will be generated if a parity
error occurs. This bit is automatically cleared to 0 whenever the UART
status register (USSR) is read.
[2]
Frame error
USSR[2] is automatically set to 1 whenever a frame error occurs during
a serial data receive operation. If the receive status interrupt enable bit,
UCON[2] is 1, a receive status interrupt will be generated if a frame
error occurs. The frame error bit is automatically cleared to 0 whenever
the UART status register (USSR) is read.
[3]
Break interrupt
USSR[3] is automatically set to 1 to indicate that a break signal has
been received. If the receive status interrupt enable bit, UCON[2], is 1,
a receive status interrupt will be generated if a break occurs.
The break interrupt bit is automatically cleared to 0 when you read
the UART status register.
[4]
–
[5]
Receive data ready
USSR[5] is automatically set to 1 whenever the receive data buffer
register (RBR) contains valid data received over the serial port. The
receive data can then be read from the RBR. When this bit is 0, the RBR
does not contain valid data. Depending on the current setting of the
SIO
receive mode bits, UCON[1:0], an interrupt or a DMA request is
generated when USSR[5] is 1.
[6]
Tx buffer register empty USSR[6] is automatically set to 1 when the transmit buffer register
(TBR)
does not contain valid data. In this case, the TBR can be written with the data to
be transmitted. When this bit is 0, the TBR contains
valid Tx data that has
not yet been copied to the transmit shift register.
In this case, the TBR
cannot be written with new Tx data. Depending on
the current setting of the
UART transmit mode bits, UCON[4:3], an
interrupt or a DMA request will be
generated whenever USSR[6] is 1.
[7]
Transmitter empty (T)
USSR[7] is automatically set to 1 when the transmit buffer register has
no valid data to transmit and when the Tx shift register is empty.
When the transmitter empty bit is 1, it indicates to software that it can
now disable the transmitter function block.