UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 320 of 841
NXP Semiconductors
UM10360
Chapter 15: LPC176x/5x UART1
15.3 Pin description
Table 288: UART1 Pin Description
Pin Type Description
RXD1 Input Serial Input. Serial receive data.
TXD1 Output
Serial Output. Serial transmit data.
CTS1 Input
Clear To Send. Active low signal indicates if the external modem is ready to accept transmitted data via
TXD1 from the UART1. In normal operation of the modem interface (U1MCR[4] = 0), the complement value
of this signal is stored in U1MSR[4]. State change information is stored in U1MSR[0] and is a source for a
priority level 4 interrupt, if enabled (U1IER[3] = 1).
Clear to send. CTS1 is an asynchronous, active low modem status signal. Its condition can be checked by
reading bit 4 (CTS) of the modem status register. Bit 0 (DCTS) of the Modem Status Register (MSR)
indicates that CTS1 has changed states since the last read from the MSR. If the modem status interrupt is
enabled when CTS1 changes levels and the auto-cts mode is not enabled, an interrupt is generated. CTS1
is also used in the auto-cts mode to control the transmitter.
DCD1 Input
Data Carrier Detect. Active low signal indicates if the external modem has established a communication
link with the UART1 and data may be exchanged. In normal operation of the modem interface
(U1MCR[4]=0), the complement value of this signal is stored in U1MSR[7]. State change information is
stored in U1MSR3 and is a source for a priority level 4 interrupt, if enabled (U1IER[3] = 1).
DSR1 Input
Data Set Ready. Active low signal indicates if the external modem is ready to establish a communications
link with the UART1. In normal operation of the modem interface (U1MCR[4] = 0), the complement value of
this signal is stored in U1MSR[5]. State change information is stored in U1MSR[1] and is a source for a
priority level 4 interrupt, if enabled (U1IER[3] = 1).
DTR1 Output Data Terminal Ready. Active low signal indicates that the UART1 is ready to establish connection with
external modem. The complement value of this signal is stored in U1MCR[0].
The DTR pin can also be used as an RS-485/EIA-485 output enable signal.
RI1 Input
Ring Indicator. Active low signal indicates that a telephone ringing signal has been detected by the
modem. In normal operation of the modem interface (U1MCR[4] = 0), the complement value of this signal is
stored in U1MSR[6]. State change information is stored in U1MSR[2] and is a source for a priority level 4
interrupt, if enabled (U1IER[3] = 1).
RTS1 Output
Request To Send. Active low signal indicates that the UART1 would like to transmit data to the external
modem. The complement value of this signal is stored in U1MCR[1].
In auto-rts mode, RTS1 is used to control the transmitter FIFO threshold logic.
Request to send. RTS1 is an active low signal informing the modem or data set that the UART is ready to
receive data. RTS1 is set to the active (low) level by setting the RTS modem control register bit and is set to
the inactive (high) level either as a result of a system reset or during loop-back mode operations or by
clearing bit 1 (RTS) of the MCR. In the auto-rts mode, RTS1 is controlled by the transmitter FIFO threshold
logic.
The RTS pin can also be used as an RS-485/EIA-485 output enable signal.
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