Nxp Semiconductors UM10237 ユーザーズマニュアル

UM10237_2

© NXP B.V. 2008. All rights reserved.

 

UART1 contains registers organized as shown in 

. The Divisor Latch Access 

Bit (DLAB) is contained in U1LCR[7] and enables access to the Divisor Latches.

RXD1 Input

 Serial receive data.

TXD1 Output Serial Output. Serial transmit data.

CTS1 Input

 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

 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

 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

 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.