MCS9845 MosChip Semiconductor, MCS9845 Datasheet - Page 20

• Manufacturer Part Number: MCS9845
• Description: PCI Dual UART
• Manufacturer: MosChip Semiconductor

Page 20
MCS9845
PCI Dual UART with ISA Bridge
Modem Status Register (MSR)
The Modem Status Register is an 8-bit register that
provides information about the current state of the
control lines from the modem, data set, or peripheral
device to the CPU.
register provide change information. When input from
the modem changes state, the appropriate bit is set to
1. All four bits are reset to 0 when the CPU reads the
Modem Status Register.
MSR Bit-0:
0 = No change to nCTS input.
1 = The nCTS input has changed state since the
MSR Bit-1:
0 = No change to nDSR input.
1 = The nDSR input has changed state since the
MSR Bit-2:
0 = No change to nRI input.
1 = The nRI input has changed from a low to a high
MSR Bit-3:
0 = No change to nCD input.
1 = The nCD input has changed state since the
last time it was read by the CPU. When the
interrupt is enabled, a Modem Status interrupt is
generated.
last time it was read by the CPU. When the
interrupt is enabled, a Modem Status interrupt is
generated.
level. When nRI is set to 1 and the interrupt is
enabled, a Modem Status interrupt is generated.
last time it was read by the CPU. When the
interrupt is enabled, a Modem Status interrupt is
generated.
Additionally, four bits of this
MSR Bit-4:
Complement of the Clear To Send (nCTS) input. When
in the diagnostic test mode, this bit is equal to nRTS.
MSR Bit-5:
Complement of the Data Set Ready (nDSR) input.
When in the diagnostic test mode, this bit is equal to
nDTR.
MSR Bit-6:
Complement of the Ring Indicator (nRI) input. When in
the diagnostic test mode, this bit is equal to nOP1.
MSR Bit-7:
Complement of the Data Carrier Detect (nCD) input.
When in the diagnostic test mode, this bit is equal to
nOP2.
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