Datasheet

UART Modules
MOTOROLA MCF5206e USER’S MANUAL 12-5
12.3 OPERATION
The following paragraphs describe the operation of the baud-rate generator, transmitter
and receiver, and other operating modes of the UART module.
12.3.1 Baud-Rate Generator/Timer
The timer references made here relative to clocking the UART are different than the
MCF5206e timer module that is integrated on the bus of the ColdFire core. The UART has
a baud generator based on an internal baud-rate timer that is dedicated to the UART. You
can program the Clock Select Register (USCR) to enable the baud-rate timer or an
external clock source from TIN to generate baud rates. When the baud-rate timer is used,
a prescaler supplies an asynchronous 32x clock source to the baud-rate timer. The baud-
rate timer register value is programmed with the UBG1 and UBG2 registers. See Section
12.4.1.12 Timer Upper Preload Register 1 (UBG1) and Section 12.4.1.13 Timer Upper
Preload Register 2 (UBG2) for more information.
An external TIN clock source, when enabled in the USCR, can generate an x1 or x16
asynchronous or synchronous clock to the UART receiver and transmitter. Figure 12-3
shows the relationship of clocking sources.
Figure 12-3. Baud-Rate Timer Generator Diagram
MCF5206e UART
MCF5206e TIMER
TIN
TOUT
TIN
SYSTEM CLOCK
x1
PRESCALAR
x16
PRESCALAR
TIMER
OUTPUT
INTERNAL
TIMER
x32
PRESCALAR
TIN
BAUD
RATE
BAUD RATE OUTPUT PROGRAMMED IN USCR
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Freescale Semiconductor, Inc.
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