ST16C550
18
Rev. 5.01
LCR BIT-6:
When enabled the Break control bit causes a break
condition to be transmitted (the TX output is forced to a
logic 0 state). This condition exists until disabled by
setting LCR bit-6 to a logic 0.
Logic 0 = No TX break condition. (normal default
condition)
Logic 1 = Forces the transmitter output (TX) to a logic
0 for alerting the remote receiver to a line break
condition.
LCR BIT-7:
The internal baud rate counter latch and Enhance
Feature mode enable.
Logic 0 = Divisor latch disabled. (normal default condi-
tion)
Logic 1 = Divisor latch and enhanced feature register
enabled.
Modem Control Register (MCR)
This register controls the interface with the modem or
a peripheral device.
MCR BIT-0:
Logic 0 = Force -DTR output to a logic 1. (normal
default condition)
Logic 1 = Force -DTR output to a logic 0.
MCR BIT-1:
Logic 0 = Force -RTS output to a logic 1. (normal
default condition)
Logic 1 = Force -RTS output to a logic 0.
MCR BIT-2:
Logic 0 = Set -OP1 output to a logic 1. (normal default
condition)
Logic 1 = Set -OP1 output to a logic 0.
MCR BIT-3:
Logic 0 = Set -OP2 output to a logic 1. (normal default
condition)
Logic 1 = Set -OP2 output to a logic 0.
MCR BIT-4:
Logic 0 = Disable loop-back mode. (normal default
condition)
Logic 1 = Enable local loop-back mode (diagnostics).
MCR BIT 5-7: Not used and set to “0”.
Line Status Register (LSR)
This register provides the status of data transfers
between. the ST16C550 and the CPU.
LSR BIT-0:
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.
LSR BIT-1:
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 addi-
tional 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 transfer into the FIFO,
therefore the data in the FIFO is not corrupted by the
error.
LSR BIT-2:
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.
LSR BIT-3:
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.
LSR BIT-4:
Logic 0 = No break condition (normal default condi-
tion)
Logic 1 = The receiver received a break signal (RX
was a logic 0 for one character frame time). In the
FIFO mode, only one break character is loaded into
the FIFO.
LSR BIT-5:
This bit is the Transmit Holding Register Empty indi-
cator. This bit indicates that the UART is ready to
accept a new character for transmission. In addition,
