SC16C751B datasheet(18/32 Pages) NXP

18 / 32 page

SC16C751B_2

Product data sheet

Rev. 02 — 10 October 2008

18 of 32

NXP Semiconductors

SC16C751B

5 V, 3.3 V and 2.5 V UART with 64-byte FIFOs

7.6 Modem Control Register (MCR)

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

The ﬂow control can be conﬁgured by programming MCR[1] and MCR[5] as shown in

Table 17.

Table 16.

Modem Control Register bits description

Bit

Symbol

Description

MCR[7]

reserved; set to 0

MCR[6]

reserved; set to 0

MCR[5]

AFE. This bit is the auto ﬂow control enable. When this bit is set, the auto

ﬂow control is enabled.

MCR[4]

Loopback. Enable the local Loopback mode (diagnostics). In this mode the

transmitter output (TX) and the receiver input (RX), CTS are disconnected

from the SC16C751B I/O pins. Internally the modem data and control pins

are connected into a loopback data conﬁguration (see Figure 4). 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 register.

logic 0 = disable Loopback mode (normal default condition)

logic 1 = enable local Loopback mode (diagnostics)

3:2

MCR[3:2]

reserved

MCR[1]

RTS

logic 0 = force RTS output to a logic 1 (normal default condition)

logic 1 = force RTS output to a logic 0

MCR[0]

reserved

Table 17.

Flow control conﬁguration

MCR[5] (AFE)

MCR[1] (RTS)

Flow conﬁguration

auto RTS and CTS enabled

auto CTS only enabled

auto RTS and CTS disabled

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