SC16C652 datasheet(24/41 Pages) PHILIPS

24 / 41 page

Philips Semiconductors

SC16C652

Dual UART with 32 bytes of transmit and receive FIFOs

Product data

Rev. 04 — 20 June 2003

24 of 41

9397 750 11634

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 SC16C652 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.

LSR[1]

Overrun error.

Logic 0 = No overrun error (normal default condition).

Logic1=Overrun error. A data overrun error occurred in the

receive shift register. This happens when additional data arrives

while the FIFO is full. In this case, the previous data in the shift

byte in the receive shift register is not transferred into the FIFO,

therefore the data in the FIFO is not corrupted by the error.

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 21:

Line Status Register bits description…continued

Bit

Symbol

Description

Table 22:

Modem Status Register bits description

Bit

Symbol

Description

MSR[7]

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).

MSR[6]

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).

MSR[5]

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).

MSR[4]

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).

MSR[3]

∆CD [1]

Logic 0 = No CD change (normal default condition).

Logic 1 = The CD input to the SC16C652 has changed state

since the last time it was read. A modem Status Interrupt will be

generated.

MSR[2]

∆RI [1]

Logic 0 = No RI change (normal default condition).

Logic 1 = The RI input to the SC16C652 has changed from a

logic 0 to a logic 1. A modem Status Interrupt will be generated.

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