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MCS7840
USB-2.0 to Four Serial Ports
Rev.
1.2
Page 17
Modem Status Register (MSR):
This register provides the status of the modem control lines to CPU.
Register:
MSR
Description:
Modem Status Register
Offset:
6
Permissions:
Read
Access Condition:
Default Value:
0x00
Bit[7]
Bit[6]
Bit[5]
Bit[4]
Bit[3]
Bit[2]
Bit[1]
Bit[0]
DCD
RI
DSR
CTS
ΔDCD
Teri
ΔDSR
ΔCTS
Bit
Description
Operation
0
Delta CTS
Logic 0:
No change in the CTS signal
Logic 1:
Indicates that the CTS input has changed since
the last time the MSR was read
1
Delta DSR
Logic 0:
No change in the DSR signal
Logic 1:
Indicates that the DSR input has changed since
the last time the MSR was read
2
Trailing Edge of RI
Logic 0:
No change in the RI signal
Logic 1:
Indicates that the RI input has changed from low
to high since the last time the MSR was read
3
Delta DCD
Logic 0:
No change in the DCD signal
Logic 1:
Indicates that the DCD input has changed since
the last time the MSR was read
4
CTS
Logic 0:
CTS# line is 1
Logic 1:
CTS# line is 0
5
DSR
Logic 0:
DSR# line is 1
Logic 1:
DSR# line is 0
6RI
Logic 0:
RI# line is 1
Logic 1:
RI# line is 0
7
DCD
Logic 0:
DCD# line is 1
Logic 1:
DCD# line is 0
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