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Philips Semiconductors
SC16C654/654D
Quad UART with 64-byte FIFO and infrared (IrDA) encoder/decoder
Product data
Rev. 02 — 13 March 2003
30 of 52
9397 750 10985
Koninklijke Philips Electronics N.V. 2003. All rights reserved.
7.8 Modem Status Register (MSR)
This register provides the current state of the control interface signals from the
modem, or other peripheral device to which the SC16C654/654D 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.
0
LSR[0]
Receive data ready.
Logic 0 = No data in receive holding register or FIFO (normal default
condition).
Logic 1 = Data has been received and is saved in the receive holding
register or FIFO.
Table 20:
Line Status Register bits description…continued
Bit
Symbol
Description
Table 21:
Modem Status Register bits description
Bit
Symbol
Description
7
MSR[7]
CD (Active-HIGH, logical 1). Normally this bit is the complement of the
CD input. In the loop-back mode this bit is equivalent to the OP2 bit in the
MCR register.
6
MSR[6]
RI (Active-HIGH, logical 1). Normally this bit is the complement of the RI
input. In the loop-back mode this bit is equivalent to the OP1 bit in the
MCR register.
5
MSR[5]
DSR (Active-HIGH, logical 1). Normally this bit is the complement of the
DSR input. In loop-back mode this bit is equivalent to the DTR bit in the
MCR register.
4
MSR[4]
CTS. CTS functions as hardware ow control signal input if it is enabled
via EFR[7]. The transmit holding register ow control is enabled/disabled
by MSR[4]. Flow control (when enabled) allows starting and stopping the
transmissions based on the external modem CTS signal. A logic 1 at the
CTS pin will stop SC16C654/654D transmissions as soon as current
character has nished transmission. Normally MSR[4] is the complement
of the CTS input. However, in the loop-back mode, this bit is equivalent to
the RTS bit in the MCR register.
3
MSR[3]
Logic 0 = No CD change (normal default condition).
Logic1=The CD input to the SC16C654/654D has changed state
since the last time it was read. A modem Status Interrupt will be
generated.
2
MSR[2]
Logic 0 = No RI change (normal default condition).
Logic1=The RI input to the SC16C654/654D has changed from a
logic 0 to a logic 1. A modem Status Interrupt will be generated.