
SC16C850
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NXP B.V. 2010. All rights reserved.
Product data sheet
Rev. 2 — 11 November 2010
30 of 55
NXP Semiconductors
SC16C850
2.5 to 3.3 V UART with 128-byte FIFOs and IrDA encoder/decoder
7.8 Modem Status Register (MSR)
This register shares the same address as EFCR register. This is a read-only register and
it provides the current state of the control interface signals from the modem, or other
peripheral device to which the SC16C850 is connected. Four bits of this register are used
to indicate the changed information. These bits are set to a logic 1 whenever a control
input from the modem changes state. These bits are set to a logic 0 whenever the CPU
reads this register.
When write, the data will be written to EFCR register.
[1]
Whenever any MSR bit 3:0 is set to logic 1, a Modem Status Interrupt will be generated.
Table 21.
Modem Status Register bits description
Bit
Symbol
Description
7
MSR[7]
CD. During normal operation, this bit is the complement of the CD input.
Reading this bit in the loopback mode produces the state of MCR[3] (OP2).
6
MSR[6]
RI. During normal operation, this bit is the complement of the RI input.
Reading this bit in the loopback mode produces the state of MCR[2] (OP1).
5
MSR[5]
DSR. During normal operation, this bit is the complement of the DSR input.
During the loopback mode, this bit is equivalent to MCR[0] (DTR).
4
MSR[4]
CTS. During normal operation, this bit is the complement of the CTS input.
During the loopback mode, this bit is equivalent to MCR[1] (RTS).
3MSR[3]
logic 0 = no CD change (normal default condition)
logic 1 = the CD input to the SC16C850 has changed state since the last
time it was read. A modem Status Interrupt will be generated.
2MSR[2]
logic 0 = no RI change (normal default condition)
logic 1 = the RI input to the SC16C850 has changed from a logic 0 to a
logic 1. A modem Status Interrupt will be generated.
1MSR[1]
logic 0 = no DSR change (normal default condition)
logic 1 = the DSR input to the SC16C850 has changed state since the
last time it was read. A modem Status Interrupt will be generated.
0MSR[0]
logic 0 = no CTS change (normal default condition)
logic 1 = the CTS input to the SC16C850 has changed state since the last
time it was read. A modem Status Interrupt will be generated.