mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 381

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
Note that when autobaud mode is enabled, the UFPDn, UDUn, and UDLn are
automatically loaded with the calculated baud rate. However, the calculated value can be
overridden by a programmed value at any time.
The choice of URT_CLK or CLKIN is programmed in the UCSR.
16.5.1.2 Calculating Baud Rates
The following sections describe how to calculate baud rates.
16.5.1.2.1 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. The
UFPD register can be used to improve the accuracy of the clock source as shown in the
following example using a 48 MHz CLKIN and 230kbs UART baud rate:
1. UART Divider = CLKIN / (16 x 2 x UART Baud Rate)
2. The truncation has resulted in an effective 8.7% error (0.52/6)
URT_RxD
URT_CLK
URT_TxD
CLKIN
= 48E06 / (32 x 230E03)
= 6.52
= 6 (truncate to lowest whole number)
UDU = 0x00, UDL = 0x06
Figure 16-23. Clocking Source Diagram
Rx Buffer
Tx Buffer
Rx
Tx
Chapter 16. UART Modules
Clocking sources programmed in UCSR
Generator
Prescaler
Prescaler
Clock
x16
x1
UART
(UFPD)
Divider
4-Bit
1-Bit Divider
(UDU, UDL)
Prescaler
16-Bit
Operation
16-21