Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 207 of 547
NXP Semiconductors
UM10398
Chapter 13: LPC111x/LPC11Cxx UART
13.5.8.1 Auto-flow control
If auto-RTS mode is enabled the UART‘s receiver FIFO hardware controls the RTS output
of the UART. If the auto-CTS mode is enabled the UART‘s U0TSR hardware will only start
transmitting if the CTS
input signal is asserted.
13.5.8.1.1 Auto-RTS
The auto-RTS function is enabled by setting the RTSen bit. Auto-RTS data flow control
originates in the U0RBR module and is linked to the programmed receiver FIFO trigger
level. If auto-RTS is enabled, the data-flow is controlled as follows:
When the receiver FIFO level reaches the programmed trigger level, RTS
is deasserted
(to a high value). It is possible that the sending UART sends an additional byte after the
trigger level is reached (assuming the sending UART has another byte to send) because it
might not recognize the deassertion of RTS
until after it has begun sending the additional
byte. RTS
is automatically reasserted (to a low value) once the receiver FIFO has reached
the previous trigger level. The reassertion of RTS
signals the sending UART to continue
transmitting data.
If Auto-RTS mode is disabled, the RTSen bit controls the RTS
output of the UART. If
Auto-RTS mode is enabled, hardware controls the RTS
output, and the actual value of
RTS
will be copied in the RTS Control bit of the UART. As long as Auto-RTS is enabled,
the value of the RTS Control bit is read-only for software.
4LMS
0
Loopback Mode Select. The modem loopback mode provides a
mechanism to perform diagnostic loopback testing. Serial data
from the transmitter is connected internally to serial input of the
receiver. Input pin, RXD, has no effect on loopback and output
pin, TXD is held in marking state. The four modem inputs (CTS
,
DSR, RI and DCD) are disconnected externally. Externally, the
modem outputs (RTS, DTR) are set inactive. Internally, the four
modem outputs are connected to the four modem inputs. As a
result of these connections, the upper four bits of the U0MSR will
be driven by the lower four bits of the U0MCR rather than the four
modem inputs in normal mode. This permits modem status
interrupts to be generated in loopback mode by writing the lower
four bits of U0MCR.
0
Disable modem loopback mode.
1 Enable modem loopback mode.
5 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
0
6 RTSEN RTS flow control 0
0 Disable auto-rts flow control.
1 Enable auto-rts flow control.
7 CTSEN CTS flow control 0
0 Disable auto-cts flow control.
1 Enable auto-cts flow control.
31:8 - - Reserved -
Table 194. UART0 Modem Control Register (U0MCR - address 0x4000 8010) bit description
Bit Symbol Value Description Reset
value