SC16C554DB datasheet(30/51 Pages) PHILIPS

30 / 51 page

9397 750 13133

Product data sheet

Rev. 01 — 9 February 2005

30 of 51

Philips Semiconductors

SC16C554B/554DB

5 V, 3.3 V and 2.5 V quad UART, 5 Mbit/s (max.) with 16-byte FIFOs

7.6 Modem Control Register (MCR)

This register controls the interface with the modem or a peripheral device.

Table 19:

Modem Control Register bits description

Bit

Symbol

Description

7:6

MCR[7:6]

Reserved; set to ‘0’.

MCR[5]

Autoﬂow control enable.

MCR[4]

Loop-back. Enable the local loop-back mode (diagnostics). In this mode

the transmitter output (TX) and the receiver input (RX), CTS, DSR, CD,

and RI are disconnected from the SC16C554B/554DB I/O pins. Internally

the modem data and control pins are connected into a loop-back data

conﬁguration (see Figure 12). In this mode, the receiver and transmitter

interrupts remain fully operational. The Modem Control Interrupts are

also operational, but the interrupts’ sources are switched to the lower four

bits of the Modem Control. Interrupts continue to be controlled by the IER

Logic 0 = Disable loop-back mode (normal default condition).

Logic 1 = Enable local loop-back mode (diagnostics).

MCR[3]

OP2, INTx enable. Used to control the modem CD signal in the loop-back

mode.

Logic 0 = Forces INTA to INTD outputs to the 3-state mode during the

16 mode (normal default condition). In the loop-back mode, sets OP2

(CD) internally to a logic 1.

Logic 1 = Forces the INTA to INTD outputs to the active mode during

the 16 mode. In the loop-back mode, sets OP2 (CD) internally to a

logic 0.

MCR[2]

OP1. This bit is used in the Loop-back mode only. In the loop-back mode,

this bit is used to write the state of the modem RI interface signal via

OP1.

MCR[1]

RTS

Logic 0 = Force RTS output to a logic 1 (normal default condition).

Logic 1 = Force RTS output to a logic 0.

Automatic RTS may be used for hardware ﬂow control by enabling

MCR[5].

MCR[0]

DTR

Logic 0 = Force DTR output to a logic 1 (normal default condition).

Logic 1 = Force DTR output to a logic 0.

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