UART Introduction
12-5
UART Devices
Table 12–1. I/O Description
Signal
I/O
Description
Reset
Value
UART/MODEM Signals
RX
I
Serial data input
–
TX
O
Serial data output
1
CTS
I
Clear to send.
Active-low modem status signal. Reading bit 4 of the modem status
register checks the condition of CTS. Reading bit 0 of that register
checks a change of state of CTS since the last read of the modem status
register. CTS is used in automatic CTS mode to control the transmitter.
–
RTS
O
Request to send.
When active (low), the module is ready to receive data. Setting modem
control register bit 1 activates RTS. It becomes inactive as a result of a
module reset, loop back mode or by clearing the MCR1. In automatic
RTS mode, it becomes inactive as a result of the receiver threshold logic.
1
DSR
I
Data set ready
Active-low modem status signal. Reading bit 5 of the modem status
register checks the condition of DSR. Reading bit 1 of that register
checks a change of state of DSR since the last read of the modem status
register.
–
DTR
O
Data transmit ready
Active-low modem control signal. Reading bit 0 of the modem control
register checks the condition of DTR.
1
IrDA Signals (UART3 Only)
RXIR
I
Serial data input
–
TXIR
O
Serial data output
0
SD_MODE
O
Signal used to configure transceivers
1