External Signal Description - Freescale Semiconductor MCF54455 Reference Manual

UART Modules
• Start/end break interrupt/status
32.2

External Signal Description

Table 32-1 briefly describes the UART module signals.
Signal
UnTXD Transmitter Serial Data Output. UnTXD is held high (mark condition) when the transmitter is
disabled, idle, or operating in the local loopback mode. Data is shifted out on UnTXD on the
falling edge of the clock source, with the least significant bit (lsb) sent first.
UnRXD Receiver Serial Data Input. Data received on UnRXD is sampled on the rising edge of the clock
source, with the lsb received first.
UnCTS Clear-to- Send. This input can generate an interrupt on a change of state.
UnRTS Request-to-Send. This output can be programmed to be negated or asserted automatically by
the receiver or the transmitter. When connected to a transmitter's UnCTS, UnRTS can control
serial data flow.
Figure 32-2 shows a signal configuration for a UART/RS-232 interface.
32.3 Memory Map/Register Definition
This section contains a detailed description of each register and its specific function. Flowcharts in
Section 32.5, "Initialization/Application
Writing control bytes into the appropriate registers controls the operation of the UART module.
UART registers are accessible only as bytes.
Interrupt can mean an interrupt request asserted to the CPU or a DMA
request.
32-3
Table 32-1. UART Module External Signals
UART
UnRTS
UnCTS
UnTXD
UnRXD
Figure 32-2. UART/RS-232 Interface
Information," describe basic UART module programming.
NOTE
NOTE
Description
RS-232 Transceiver
DI2
DO2
DI1
DO1
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