sc68c2550b NXP Semiconductors, sc68c2550b Datasheet - Page 21

• Manufacturer Part Number: sc68c2550b
• Description: Sc68c2550b 5 V, 3.3 V And 2.5 V Dual Uart, 5 Mbit/s Max. , With 16-byte Fifos And Motorola Up Interface
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14941
Product data sheet
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 SC68C2550B 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.
Table 19:
[1]
Bit
7
6
5
4
3
2
1
0
Whenever any MSR bit 0 to bit 3 is set to logic 1, a Modem Status Interrupt will be generated.
Symbol
MSR[7]
MSR[6]
MSR[5]
MSR[4]
MSR[3]
MSR[2]
MSR[1]
MSR[0]
Modem Status Register bits description
5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 16-byte FIFOs
Description
CD. During normal operation, this bit is the complement of the CD input.
Reading this bit in the Loop-back mode produces the state of MCR[3] (OP2).
RI. During normal operation, this bit is the complement of the RI input.
Reading this bit in the Loop-back mode produces the state of MCR[2] (OP1).
DSR. During normal operation, this bit is the complement of the DSR input.
During the Loop-back mode, this bit is equivalent to MCR[0] (DTR).
CTS. During normal operation, this bit is the complement of the CTS input.
During the Loop-back mode, this bit is equivalent to MCR[1] (RTS).
CD
RI
DSR
CTS
logic 0 = no CD change (normal default condition)
logic 1 = the CD input to the SC68C2550B has changed state since the
last time it was read. A Modem Status Interrupt will be generated.
logic 0 = no RI change (normal default condition)
logic 1 = the RI input to the SC68C2550B has changed from a logic 0 to a
logic 1. A Modem Status Interrupt will be generated.
logic 0 = no DSR change (normal default condition)
logic 1 = the DSR input to the SC68C2550B has changed state since the
last time it was read. A Modem Status Interrupt will be generated.
logic 0 = no CTS change (normal default condition)
logic 1 = the CTS input to the SC68C2550B has changed state since the
last time it was read. A Modem Status Interrupt will be generated.
Rev. 02 — 28 April 2005
[1]
[1]
[1]
[1]
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
SC68C2550B
21 of 35