UART Modules
MCF52277 Reference Manual, Rev. 1
30-18
Freescale Semiconductor
Using a 83-MHz internal bus clock and letting baud rate equal 9600, then
Eqn. 30-2
Therefore, UBG1
n
equals 0x01 and UBG2
n
equals 0x0E.
30.4.1.2.2
External Clock
An external source clock (DT
n
IN) passes through a divide-by-1 or 16 prescaler. If f
extc
is the external clock
frequency, baud rate can be described with this equation:
Eqn. 30-3
30.4.2
Transmitter and Receiver Operating Modes
is a functional block diagram of the transmitter and receiver showing the command and
operating registers, which are described generally in the following sections. For detailed descriptions, refer
to
Section 30.3, “Memory Map/Register Definition
.”
Figure 30-18. Transmitter and Receiver Functional Diagram
30.4.2.1
Transmitter
The transmitter is enabled through the UART command register (UCR
n
). When it is ready to accept a
character, UART sets USR
n
[TXRDY]. The transmitter converts parallel data from the CPU to a serial bit
stream on U
n
TXD. It automatically sends a start bit followed by the programmed number of data bits, an
Divider
83
MHz
32 x 9600
[
]
-------------------------------
270 decimal
(
)
0x
010
E
hexadecimal
(
)
=
=
=
Baudrate
f
extc
(16 or 1)
---------------------
=
Receiver Shift Register
UART Command Register (UCR
n
)
W
UART Status Register (USR
n
)
R
Transmitter Shift Register
UART Mode Register 1 (UMR1
n
)
R/W
UART Mode Register 2 (UMR2
n
)
R/W
Transmitter Holding Register
W
Receiver Holding Register 3
Receiver Holding Register 2
Receiver Holding Register 1
R
UART Receive
UART
Buffer (URB
n
)
(4 Registers)
UART
n
External
Interface
Transmit Buffer
(UTB
n
)
(2 Registers)
FIFO
U
n
RXD
U
n
TXD
Содержание MCF52277
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