Chapter 16. UART Modules
16-21
Operation
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.
Figure 16-23. Clocking Source Diagram
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)
= 48E06 / (32 x 230E03)
= 6.52
= 6 (truncate to lowest whole number)
UDU = 0x00, UDL = 0x06
2. The truncation has resulted in an effective 8.7% error (0.52/6)
UART
x1
Prescaler
x16
Prescaler
Clock
Generator
4-Bit
Divider
16-Bit
Prescaler
Clocking sources programmed in UCSR
URT_CLK
URT_TxD
URT_RxD
Tx
Rx
Rx Buffer
Tx Buffer
CLKIN
1-Bit Divider
(UDU, UDL)
(UFPD)
Summary of Contents for DigitalDNA ColdFire MCF5272
Page 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Page 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Page 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Page 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Page 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Page 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Page 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Page 338: ...13 44 MCF5272 User s Manual Application Examples ...
Page 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Page 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Page 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Page 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...