UM10503
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User manual
Rev. 1.3 — 6 July 2012
984 of 1269
NXP Semiconductors
UM10503
Chapter 38: LPC43xx UART1
38.5 Pin description
Table 847: UART1 Pin description
Pin
function
Direction
Description
U1_RXD
Input
Serial Input.
Serial receive data.
U1_TXD
Output
Serial Output.
Serial transmit data.
U1_CTS
Input
Clear To Send.
Active low signal indicates if the external modem is ready to accept transmitted
data via TXD from the UART1. In normal operation of the modem interface (MCR[4] = 0), the
complement value of this signal is stored in MSR[4]. State change information is stored in MSR[0]
and is a source for a priority level 4 interrupt, if enabled (IER[3] = 1).
Clear to send. CTS 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 CTS has changed states since the last read from the MSR. If the
modem status interrupt is enabled when CTS changes levels and the auto-cts mode is not enabled,
an interrupt is generated. CTS is also used in the auto-cts mode to control the transmitter.
U1_DCD
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 (MCR[4]=0), the complement value of this signal is stored in MSR[7]. State
change information is stored in MSR3 and is a source for a priority level 4 interrupt, if enabled
(IER[3] = 1).
U1_DSR
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 (MCR[4] = 0), the
complement value of this signal is stored in MSR[5]. State change information is stored in MSR[1]
and is a source for a priority level 4 interrupt, if enabled (IER[3] = 1).
U1_DTR
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 MCR[0].
The DTR pin can also be used as an RS-485/EIA-485 output enable signal.
U1_RI
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 (MCR[4] = 0), the complement value of this
signal is stored in MSR[6]. State change information is stored in MSR[2] and is a source for a
priority level 4 interrupt, if enabled (IER[3] = 1).
U1_RTS
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 MCR[1].
In auto-rts mode, RTS is used to control the transmitter FIFO threshold logic.
Request to send. RTS is an active low signal informing the modem or data set that the UART is
ready to receive data. RTS 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, RTS is controlled by
the transmitter FIFO threshold logic.
The RTS pin can also be used as an RS-485/EIA-485 output enable signal.