SC68C2550B_3 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 03 — 9 October 2009 20 of 36
NXP Semiconductors
SC68C2550B
5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 16-byte FIFOs
7.7 Line Status Register (LSR)
This register provides the status of data transfers between the SC68C2550B and
the CPU.
Table 18. Line Status Register bits description
Bit Symbol Description
7 LSR[7] FIFO data error
logic 0 = no error (normal default condition)
logic 1 = at least one parity error, framing error or break indication is in the
current FIFO data. This bit is cleared when there are no remaining error flags
associated with the remaining data in the FIFO.
6 LSR[6] THR and TSR empty. This bit is the Transmit Empty indicator. This bit is set to a
logic 1 whenever the Transmit Holding Register and the Transmit Shift Register
are both empty. It is reset to logic 0 whenever either the THR or TSR contains a
data character. In the FIFO mode, this bit is set to ‘1’ whenever the transmit FIFO
and transmit shift register are both empty.
5 LSR[5] THR empty. This bit is the Transmit Holding Register Empty indicator. This bit
indicates that the UART is ready to accept a new character for transmission. In
addition, this bit causes the UART to issue an interrupt to CPU when the THR
interrupt enable is set. The THR bit is set to a logic 1 when a character is
transferred from the Transmit Holding Register into the Transmit Shift Register.
The bit is reset to a logic 0 concurrently with the loading of the Transmit Holding
Register by the CPU. In the FIFO mode, this bit is set when the transmit FIFO is
empty; it is cleared when at least 1 byte is written to the transmit FIFO.
4 LSR[4] Break interrupt
logic 0 = no break condition (normal default condition)
logic 1 = the receiver received a break signal (RXn was a logic 0 for one
character frame time). In the FIFO mode, only one break character is loaded
into the FIFO.
3 LSR[3] Framing error
logic 0 = no framing error (normal default condition)
logic 1 = framing error. The receive character did not have a valid stop bit(s). In
the FIFO mode, this error is associated with the character at the top of the
FIFO.
2 LSR[2] Parity error
logic 0 = no parity error (normal default condition)
logic 1 = parity error. The receive character does not have correct parity
information and is suspect. In the FIFO mode, this error is associated with the
character at the top of the FIFO.
1 LSR[1] Overrun error
logic 0 = no overrun error (normal default condition)
logic 1 = overrun error. A data overrun error occurred in the receive shift
register. This happens when additional data arrives while the FIFO is full. In
this case, the previous data in the shift register is overwritten. Note that under
this condition, the data byte in the Receive Shift Register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error.
0 LSR[0] Receive data ready
logic 0 = no data in Receive Holding Register or FIFO (normal default
condition)
logic 1 = data has been received and is saved in the Receive Holding Register
or FIFO
