mcf5407 Freescale Semiconductor, Inc, mcf5407 Datasheet - Page 366

• Manufacturer Part Number: mcf5407
• Description: Mcf5407 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Operation
14.5.1.1 Programmable Divider
As Figure 14-28 shows, the UART transmitter and receiver can use the following clock
sources:
The choice of TIN or CLKIN is programmed in the UCSR.
14.5.1.2 Calculating Baud Rates
The following sections describe how to calculate baud rates.
14.5.1.2.1 CLKIN Baud Rates
When CLKIN is the UART clocking source, it goes through a divide-by-32 prescaler and
then passes through the 16-bit divider of the concatenated UDUn and UDLn registers.
Using a 54-MHz CLKIN, the baud-rate calculation is as follows:
14-24
• An external clock signal on the TIN pin that can be divided by 16. When not divided,
• CLKIN supplies an asynchronous clock source that is divided by 32 and then
TIN provides a synchronous clock mode; when divided by 16, it is asynchronous.
divided by the 16-bit value programmed in UDUn and UDLn. See Section 14.3.16,
“UART Divider Upper/Lower Registers (UDUn/UDLn).”
CLKIN
TOUT
RxD
TxD
TIN
If TIN is a clocking source for either the timer or UART, as is
the case for UART1 used as an 8- or 16-bit CODEC interface,
the timer module cannot use TIN for timer capture.
Figure 14-28. Clocking Source Diagram
Rx Buffer
Tx Buffer
Rx
Tx
Timer Module
On-Chip
MCF5407 User’s Manual
Clocking sources programmed in UCSR
NOTE:
Generator
Prescaler
Prescaler
Clock
x16
x1
UART
TIN
TIN
Divider
16-Bit
Prescaler
x32