NXP Semiconductors LPC24XX UM10237 - Manual (Page 444)

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User manual Rev. 04 — 26 August 2009 444 of 792
NXP Semiconductors
UM10237
Chapter 17: LPC24XX UART1
3. Pin description
4. Register description
UART1 contains registers organized as shown in Table 17–396 . The Divisor Latch Access
Bit (DLAB) is contained in U1LCR[7] and enables access to the Divisor Latches.
Table 395: 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).
Only CTS1 is also used in auto-cts mode to control the UART1 transmitter.
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].
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].
Only in the auto-rts mode uses RTS1 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.