ST16C554 datasheet(21/39 Pages) EXAR

21 / 39 page

ST16C554/554D

REV. 4.0.1

2.97V TO 5.5V QUAD UART WITH 16-BYTE FIFO

LCR[5]: TX and RX Parity Select

If the parity bit is enabled, LCR BIT-5 selects the forced parity format.

• LCR BIT-5 = logic 0, parity is not forced (default).

• LCR BIT-5 = logic 1 and LCR BIT-4 = logic 0, parity bit is forced to HIGH for the transmit and receive data.

• LCR BIT-5 = logic 1 and LCR BIT-4 = logic 1, parity bit is forced to LOW for the transmit and receive data.

LCR[6]: Transmit Break Enable

When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a

“space’, logic 0, state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.

• Logic 0 = No TX break condition. (default)

• Logic 1 = Forces the transmitter output (TX) to a “space”, logic 0, for alerting the remote receiver of a line

break condition.

LCR[7]: Baud Rate Divisors Enable

Baud rate generator divisor (DLL/DLM) enable.

• Logic 0 = Data registers are selected (default).

• Logic 1 = Divisor latch registers are selected.

4.7

Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write

The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs.

MCR[0]: DTR# Output

The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a

general purpose output.

• Logic 0 = Force DTR# output HIGH (default).

• Logic 1 = Force DTR# output LOW.

MCR[1]: RTS# Output

The RTS# pin is a modem control output. If the modem interface is not used, this output may be used as a

general purpose output.

• Logic 0 = Force RTS# output HIGH (default).

• Logic 1 = Force RTS# output LOW.

MCR[2]: Reserved

OP1# is not available as an output pin on the 554. But it is available for use during Internal Loopback Mode. In

the Loopback Mode, this bit is used to write the state of the modem RI# interface signal.

TABLE 11: PARITY SELECTION

LCR BIT-5 LCR BIT-4 LCR BIT-3

PARITY SELECTION

No parity

Odd parity

Even parity

Force parity to mark, HIGH

Forced parity to space, LOW

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