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D-39
SYSTEM REGISTER QUICK REFERENCE
D.36 MSR
n
Modem Status
MSR0, MSR1
(read only)
Expanded Addr:
ISA Addr:
Reset State:
MSR0 MSR1
F4FEH F8FEH
03FEH 02FEH
X0H X0H
7 0
DCD RI DSR CTS DDCD TERI DDSR DCTS
Bit
Number
Bit
Mnemonic
Function
7 DCD Data Carrier Detect:
This bit is the complement of the data carrier detect (DCD
n
#) input. In
diagnostic test mode, this bit is equivalent to MCR
n
.3 (OUT2).
6 RI Ring Indicator:
This bit is the complement of the ring indicator (RI
n
#) input. In diagnostic
test mode, this bit is equivalent to MCR
n
.2 (OUT1).
5 DSR Data Set Ready:
This bit is the complement of the data set ready (DSR
n
#) input. In
diagnostic test mode, this bit is equivalent to MCR
n
.0 (DTR).
4 CTS Clear to Send:
This bit is the complement of the clear to send (CTS
n
#) input. In
diagnostic test mode, this bit is equivalent to MCR
n
.1 (RTS).
3 DDCD Delta Data Carrier Detect:
When set, this bit indicates that the DCD
n
# input has changed state
since the last time this register was read. Reading this register clears
this bit.
2 TERI Trailing Edge Ring Indicator:
When set, this bit indicates that the RI
n
# input has changed from a low
to a high state since the last time this register was read. Reading this
register clears this bit.
1 DDSR Delta Data Set Ready:
When set, this bit indicates that the DSR
n
# input has changed state
since the last time this register was read. Reading this register clears
this bit.
0 DCTS Delta Clear to Send:
When set, this bit indicates that the CTS
n
# input has changed state
since the last time this register was read. Reading this register clears
this bit.