MOTOROLA
UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER MODULE
MMC2001
11-2
REFERENCE MANUAL
Figure 11-1 UART Channel Block Diagram
11.2 UART Signals
11.2.1 RTS — Request to Send (UART0)
An external device requests data from the UART by asserting the RTS input. When
the ignore RTS (IRTS) bit is set, the UART ignores the RTS input and sends a charac-
ter whenever a character is ready to transmit.
If RTS goes high during transmission, the UART finishes sending the current charac-
ter and then shuts off. FIFO content (characters to be transmitted) is undisturbed.
Any transition on the pin can cause an interrupt request to wake up the MCU from low
power state. Interrupts are enabled by the RTSD EN bit in UART control register 1.
This pin can also be used as a general-purpose input whose status is read in the
RTSS bit in the UART status register.
11.2.2 CTS — Clear to Send (UART0)
The UART signals an external device that it is ready to receive data by asserting the
CTS output. If the receiver detects a pending overrun, it negates the CTS output.
This pin can also be used as a general purpose output controlled by the CTS bit in
UART control register 2.
Transmitter
Data Path
Receiver
Data Path
RxD
TxD
RTS
CTS
M
odu
le
Inte
rf
a
c
e
G
a
sk
e
t B
loc
k
16x Bit Clock
Generator
16.38MHz
TX F
IFO
RX F
IFO
P
e
ri
ph
er
al
G
as
k
et B
lo
c
k
Data
Control
DCE I
n
terf
ace
In
fr
ared Inte
rf
ac
e
HI_REF_CLK
Freescale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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