Chapter 16. UART Modules
16-23
Operation
16.5.2 Transmitter and Receiver Operating Modes
Figure 16-24 is a functional block diagram of the transmitter and receiver showing the
command and operating registers, which are described generally in the following sections
and described in detail in Section 16.3, “Register Descriptions.”
Figure 16-24. Transmitter and Receiver Functional Diagram
16.5.2.1 Transmitting
The transmitter is enabled through the UART command register (UCRn). When it is ready
to accept a character, the UART sets USRn[TxRDY]. The transmitter converts parallel data
from the CPU to a serial bit stream on TxD. It automatically sends a start bit followed by
the programmed number of data bits, an optional parity bit, and the programmed number
of stop bits. The lsb is sent first. Data is shifted from the transmitter output on the falling
edge of the clock source.
After the stop bits are sent, if no new character is in the transmitter holding register, the TxD
output remains high (mark condition) and the transmitter empty bit, USRn[TxEMP], is set.
Transmission resumes and TxEMP is cleared when the CPU loads a new character into the
UART transmitter buffer (UTBn). If the transmitter receives a disable command, it
continues until any character in the transmitter shift register is completely sent.
If the transmitter is reset through a software command, operation stops immediately (see
Section 16.3.5, “UART Command Registers (UCRn)”). The transmitter is reenabled
through the UCRn to resume operation after a disable or software reset.
UART Command Register (UCR0)
W
UART Status Register (USR0)
R
Transmitter Shift Register
UART Mode Register 1 (UMR1)
R/W
UART Mode Register 2 (UMR2)
R/W
Transmitter FIFO
W
Receiver Shift Register
Receiver FIFO
R
UART
External
Interface
RXD
TXD
UART Transmit
FIFO (URB)
(24 Bytes)
UART Transmit
FIFO (URB)
(24 Bytes)
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
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Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
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Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...