16-20
MCF5272 User’s Manual
Operation
Figure 16-22 shows a signal configuration for a UART/RS-232 interface.
Figure 16-22. UART/RS-232 Interface
16.5 Operation
This section describes operation of the clock source generator, transmitter, and receiver.
16.5.1 Transmitter/Receiver Clock Source
CLKIN serves as the basic timing reference for the clock source generator logic, which
consists of a clock generator and a programmable 16+4-bit divider (UDU, UDL, UFPD)
dedicated to the UART. The clock generator cannot produce standard baud rates if CLKIN
is used, so the 16-bit divider should be used.
16.5.1.1 Programmable Divider
As Figure 16-23 shows, the UART transmitter and receiver can use the following clock
sources:
•
An external clock signal on the URT_CLK pin that can be divided by 16. When not
divided, URT_CLK provides a synchronous clock mode; when divided by 16, it is
asynchronous.
•
CLKIN supplies an asynchronous clock source that is prescaled by 32 and then
divided by the 16-bit value programmed in UDUn and UDLn. See Section 16.3.11,
“UART Divider Upper/Lower Registers (UDUn/UDLn).” The precision of this
clock source can be tuned using the 4-bit value programmed in UFPDn.
Request-to-
Send (URT_RTS)
This output can be programmed to be negated or asserted automatically by either the receiver
or the transmitter. It can control serial data flow when connected to a transmitter’s CTS.
Clock (URT_CLK)
The UART’s external clock source. It can be used in 1x or 16x mode. When both the transmitter
and receiver use the timer as the clock source (UCR = 0xDD), the 16x clock is driven out on
UARTCLK. If either the transmitter or receiver use an external clock (1x or 16x), URT_CLK is an
input.
Table 16-15. UART Module Signals (Continued)
Signal
Description
DO2
DI1
DI2
DO1
RS-232 Transceiver
UART
URT_RTS
URT_CTS
URT_TxD
URT_RxD
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 ...