
Philips Semiconductors
SC16C550
Universal Asynchronous Receiver/Transmitter (UART)
with 16-byte FIFO and infrared (IrDA) encoder/decoder
Product data
Rev. 04 — 13 March 2003
27 of 52
9397 750 11206
Koninklijke Philips Electronics N.V. 2003. All rights reserved.
7.6 Modem Control Register (MCR)
This register controls the interface with the modem or a peripheral device.
Table 18:
Modem Control Register bits description
Bit
Symbol
Description
7
MCR[7]
Reserved; set to ‘0’.
6
MCR[6]
IR enable.
Logic 0 = Enable the standard modem receive and transmit
input/output interface (normal default condition).
Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs.
While in this mode, the TX/RX output/inputs are routed to the
infrared encoder/decoder. The data input and output levels will
conform to the IrDA infrared interface requirement. As such, while
in this mode, the infrared TX output will be a logic 0 during idle data
conditions.
5
MCR[5]
Reserved; set to ‘0’.
Use EFR[6,7] to enable Auto RTS, CTS ow control.
4
MCR[4]
Loop-back. Enable the local loop-back mode (diagnostics). In this
mode the transmitter output (TX) and the receiver input (RX), CTS,
DSR, DCD, and RI are disconnected from the SC16C550 I/O pins.
Internally the modem data and control pins are connected into a
loop-back data conguration (see
Figure 10). In this mode, the
receiver and transmitter interrupts remain fully operational. The
Modem Control Interrupts are also operational, but the interrupts’
sources are switched to the lower four bits of the Modem Control.
Interrupts continue to be controlled by the IER register.
Logic 0 = Disable loop-back mode (normal default condition).
Logic 1 = Enable local loop-back mode (diagnostics).
3
MCR[3]
OUT2, INTx enable. Used to control the modem DCD signal in the
loop-back mode.
Logic 0 = Forces INT output to the 3-State mode. In the loop-back
mode, sets OUT2 (DCD) internally to a logic 1.
Logic 1 = Forces the INT output to the active mode. In the
loop-back mode, sets OUT2 (DCD) internally to a logic 0.
2
MCR[2]
OUT1. This bit is used in the Loop-back mode only. In the loop-back
mode, this bit is used to write the state of the modem RI interface
signal via OUT1.
1
MCR[1]
RTS
Logic0=Force RTS output to a logic 1 (normal default condition).
Logic1=Force RTS output to a logic 0.
0
MCR[0]
DTR
Logic 0 = Force DTR output to a logic 1 (normal default condition).
Logic 1 = Force DTR output to a logic 0.