XR19L400_09 Datasheet, PDF (29/46 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER

XR19L400
REV. 1.0.3
SINGLE CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER
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
DTR# is not available as an output pin on the L400, but it is available for use during internal loopback mode. In
internal loopback mode, this bit is used to write the state of the DSR# interface signal.
• Logic 0 = Force DTR# output HIGH (default).
• Logic 1 = Force DTR# output LOW.
MCR[1]: RTS# Output
RTS# is not available as an output pin on the L400, but it is available for use during internal loopback mode. In
internal loopback mode, this bit is used to write the state of the CTS# interface signal. If half-duplex mode is
enabled via the Half/Full# pin or in is a modem control output and may be used for automatic hardware flow
control by enabled by EFR bit-6. The RTS# pin can also be used for Auto RS485 Half-Duplex direction control
enabled by FCTR bit-3. If the modem interface is not used, this output may be used as a general purpose
output.
• Logic 0 = Force RTS# HIGH (default).
• Logic 1 = Force RTS# LOW.
MCR[2]: Reserved
OP1# is not available as an output pin on the L400. 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.
MCR[3]: OP2# Output / INT Output Enable
This bit enables or disables the operation of INT, interrupt output. If INT output is not used, OP2# can be used
as a general purpose output. Also, if 16/68# pin selects Motorola bus interface mode, this bit must be set to
logic 0.
• Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set HIGH(default).
• Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set LOW.
MCR[4]: Internal Loopback Enable
• Logic 0 = Disable loopback mode (default).
• Logic 1 = Enable local loopback mode, see loopback section and Figure 11.
MCR[5]: Xon-Any Enable (requires EFR bit-4=1)
• Logic 0 = Disable Xon-Any function (default).
• Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO, unless the RX character is an Xon or Xoff character and
the L400 is programmed to use the Xon/Xoff flow control.
MCR[6]: Reserved
For normal operation, this bit should remain a logic 0.
MCR[7]: Clock Prescaler Select (requires EFR bit-4=1)
• Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
• Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth.
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