Registers
1528
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Asynchronous Receiver/Transmitter (UART)
31.3.9 Modem Status Register (MSR)
The Modem status register (MSR) is shown in
and described in
. MSR provides
information to the CPU concerning the status of modem control signals. MSR is intended for read
operations only; do not write to this register.
Figure 31-17. Modem Status Register (MSR)
31
16
Reserved
R-0
15
8
7
6
5
4
3
2
1
0
Reserved
CD
RI
DSR
CTS
DCD
TERI
DDSR
DCTS
R-0
R-0
R-0
R-0
R-0
R-0
R-0
R-0
R-0
LEGEND: R = Read only; -
n
= value after reset
Table 31-18. Modem Status Register (MSR) Field Descriptions
Bit
Field
Value
Description
31-8
Reserved
0
Reserved
7
CD
0
Complement of the Carrier Detect input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 3 (OUT2).
6
RI
0
Complement of the Ring Indicator input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 2 (OUT1).
5
DSR
0
Complement of the Data Set Ready input. When the UART is in the diagnostic test mode (loopback
mode MCR[4] = 1), this bit is equal to the MCR bit 0 (DTR).
4
CTS
0
Complement of the Clear To Send input. When the UART is in the diagnostic test mode (loopback
mode MCR[4] = 1), this bit is equal to the MCR bit 1 (RTS).
3
DCD
0
Change in DCD indicator bit. DCD indicates that the DCD input has changed state since the last time it
was read by the CPU. When DCD is set and the modem status interrupt is enabled, a modem status
interrupt is generated.
2
TERI
0
Trailing edge of RI (TERI) indicator bit. TERI indicates that the RI input has changed from a low to a
high. When TERI is set and the modem status interrupt is enabled, a modem status interrupt is
generated.
1
DDSR
0
Change in DSR indicator bit. DDSR indicates that the DSR input has changed state since the last time it
was read by the CPU. When DDSR is set and the modem status interrupt is enabled, a modem status
interrupt is generated.
0
DCTS
0
Change in CTS indicator bit. DCTS indicates that the CTS input has changed state since the last time it
was read by the CPU. When DCTS is set (autoflow control is not enabled and the modem status
interrupt is enabled), a modem status interrupt is generated. When autoflow control is enabled, no
interrupt is generated.