DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
280 of 571
NXP Semiconductors
UM10316
Chapter 19: LPC29xx Universal Asynchronous Receiver/Transmitter
4.8.1 Auto-flow control
If auto-RTS mode is enabled the UART0/1‘s receiver FIFO hardware controls the RTS
output of the UART. If the auto-CTS mode is enabled the UART0/1‘s TSR hardware will
only start transmitting if the CTS input signal is asserted.
19.4.8.2
Auto-RTS
The auto-RTS function is enabled by setting the RTSen bit. Auto-RTS data flow control
originates in the RBR 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 RTS1 signals to 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.
4
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,
RXD1, 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 MSR will be driven by the
lower four bits of the MCR 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
U1MCR.
0
0
Disable modem loopback mode.
1
Enable modem loopback mode.
5
-
NA
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
0
6
RTSen
0
Disable auto-rts flow control.
0
1
Enable auto-rts flow control.
7
CTSen
0
Disable auto-cts flow control.
0
1
Enable auto-cts flow control.
Table 238: UART0/1 Modem Control Register (U0MCR - address 0xE004 5010,
U1MCR - 0xE004 6010) bit description
Bit
Symbol
Value Description
Reset
value