MSR

         Modem Status Register
It should be noted that whenever bits 0, 1, 2 or 3 is set to logic one, to indicate
a change on the modem control inputs, a modem status interrupt will be generated
if enabled via the IER regardless of when the change occurred. Since the delta bits
(bits 0, 1, 3) can get set after a reset if their respective modem signals are
active (see individual bits for details), a read of the MSR after reset can be
performed to prevent unwanted interrupts.

Module Instance	Base Address	Register Address
`i_uart_uart_address_block`	`0xFF8D0000`	`0xFF8D0018`

Size: 32

Offset: 0x18

Access: RO

Important: The value of a reserved bit must be maintained in software. When you modify registers containing reserved bit fields, you must use a read-modify-write operation to preserve state and prevent indeterminate system behavior.

Bit Fields
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16
`RSVD_MSR_31to8` `RO 0x0`
15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
`RSVD_MSR_31to8` `RO 0x0`								`DCD` `RO 0x0`	`RI` `RO 0x0`	`DSR` `RO 0x0`	`CTS` `RO 0x0`	`DDCD` `RO 0x0`	`TERI` `RO 0x0`	`DDSR` `RO 0x0`	`DCTS` `RO 0x0`

MSR Fields

Bit

Name

Description

Access

Reset

31:8

RSVD_MSR_31to8

Reserved bits [31:8] - Read Only

RO

0x0

DCD

Data Carrier Detect.
This is used to indicate the current state of the modem control line dcd_n. That is
this bit is the complement dcd_n. When the Data Carrier Detect input (dcd_n) is
asserted it is an indication that the carrier has been detected by the modem or
data set.
0 = dcd_n input is de-asserted (logic 1)
1 = dcd_n input is asserted (logic 0)
In Loopback Mode (MCR[4] set to one), DCD is the same as MCR[3] (Out2).

Value	Description
0x0	dcd_n input is de-asserted (logic 1)
0x1	dcd_n input is asserted (logic 0)

RO

0x0

RI

Ring Indicator.
This is used to indicate the current state of the modem control line ri_n. That is
this bit is the complement ri_n. When the Ring Indicator input (ri_n) is asserted
it is an indication that a telephone ringing signal has been received by the modem
or data set.
0 = ri_n input is de-asserted (logic 1)
1 = ri_n input is asserted (logic 0)
In Loopback Mode (MCR[4] set to one), RI is the same as MCR[2] (Out1).

Value	Description
0x0	ri_n input is de-asserted (logic 1)
0x1	ri_n input is asserted (logic 0)

RO

0x0

DSR

Data Set Ready.
This is used to indicate the current state of the modem control line dsr_n. That is
this bit is the complement dsr_n. When the Data Set Ready input (dsr_n) is asserted
it is an indication that the modem or data set is ready to establish communications
with the DW_apb_uart.
0 = dsr_n input is de-asserted (logic 1)
1 = dsr_n input is asserted (logic 0)
In Loopback Mode (MCR[4] set to one), DSR is the same as MCR[0] (DTR).

Value	Description
0x0	dsr_n input is de-asserted (logic 1)
0x1	dsr_n input is asserted (logic 0)

RO

0x0

CTS

Clear to Send.
This is used to indicate the current state of the modem control line cts_n. That is,
this bit is the complement cts_n. When the Clear to Send input (cts_n) is asserted
it is an indication that the modem or data set is ready to exchange data with the
DW_apb_uart.
0 = cts_n input is de-asserted (logic 1)
1 = cts_n input is asserted (logic 0)
In Loopback Mode (MCR[4] set to one), CTS is the same as MCR[1] (RTS).

Value	Description
0x0	cts_n input is de-asserted (logic 1)
0x1	cts_n input is asserted (logic 0)

RO

0x0

DDCD

Delta Data Carrier Detect.
This is used to indicate that the modem control line dcd_n has changed since the last
time the MSR was read. That is:
0 = no change on dcd_n since last read of MSR
1 = change on dcd_n since last read of MSR
Reading the MSR clears the DDCD bit.
In Loopback Mode (MCR[4] set to one), DDCD reflects changes on MCR[3] (Out2).
Note, if the DDCD bit is not set and the dcd_n signal is asserted (low) and a reset
occurs (software or otherwise), then the DDCD bit will get set when the reset is
removed if the dcd_n signal remains asserted.

Value	Description
0x0	No change on dcd_n since last read of MSR
0x1	change on dcd_n since last read of MSR

RO

0x0

TERI

Trailing Edge of Ring Indicator.
This is used to indicate that a change on the input ri_n (from an active low, to
an inactive high state) has occurred since the last time the MSR was read. That is:
0 = no change on ri_n since last read of MSR
1 = change on ri_n since last read of MSR
Reading the MSR clears the TERI bit.
In Loopback Mode (MCR[4] set to one), TERI reflects when MCR[2] (Out1) has changed
state from a high to a low.

Value	Description
0x0	No change on ri_n since last read of MSR
0x1	change on ri_n since last read of MSR

RO

0x0

DDSR

Delta Data Set Ready.
This is used to indicate that the modem control line dsr_n has changed since
the last time the MSR was read. That is:
0 = no change on dsr_n since last read of MSR
1 = change on dsr_n since last read of MSR
Reading the MSR clears the DDSR bit.
In Loopback Mode (MCR[4] set to one), DDSR reflects changes on MCR[0] (DTR).
Note, if the DDSR bit is not set and the dsr_n signal is asserted (low) and a reset
occurs (software or otherwise), then the DDSR bit will get set when the reset is
removed if the dsr_n signal remains asserted.

Value	Description
0x0	No change on dsr_n since last read of MSR
0x1	change on dsr_n since last read of MSR

RO

0x0

DCTS

Delta Clear to Send.
This is used to indicate that the modem control line cts_n has changed since the
last time the MSR was read. That is:
0 = no change on cts_n since last read of MSR
1 = change on cts_n since last read of MSR
Reading the MSR clears the DCTS bit.
In Loopback Mode (MCR[4] set to one), DCTS reflects changes on MCR[1] (RTS).
Note, if the DCTS bit is not set and the cts_n signal is asserted (low) and a reset
occurs (software or otherwise), then the DCTS bit will get set when the reset is
removed if the cts_n signal remains asserted.

Value	Description
0x0	No change on cts_n since last read of MSR
0x1	change on cts_n since last read of MSR

RO

0x0