mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 380

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

Operation
Figure 16-22 shows a signal configuration for a 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:
16-20
Request-to-
Send (URT_RTS)
Clock (URT_CLK)
• An external clock signal on the URT_CLK pin that can be divided by 16. When not
• CLKIN supplies an asynchronous clock source that is prescaled by 32 and then
Signal
divided, URT_CLK 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 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.
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.
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)
Figure 16-22. UART/RS-232 Interface
URT_CTS
URT_RTS
URT_RxD
URT_TxD
UART
MCF5272 User’s Manual
Description
RS-232 Transceiver
DI2
DO2
DI1
DO1
MOTOROLA