mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 650

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

Communication Processor Module
16.9.15 The SCCs in UART Mode
Many applications need a simple method of sending low-speed data between pieces of
equipment. The universal asynchronous receiver transmitter (UART) protocol is the de-facto
standard for such communication. The term asynchronous is used because it is not
necessary to send clocking information along with the data being sent. UART links are
character-oriented. Asynchronous links are used to connect terminals and other computer
equipment together. Even in applications where synchronous communication is required,
the UART is often used for a local debugging port to run board debugger software. The
character format of the UART protocol is illustrated in Figure 16-72.
Since the transmitter and receiver operate asynchronously, there is no need to connect the
transmit and receive clocks. Instead, the receiver oversamples the incoming datastream
(usually by a factor of 16) and uses some of these samples to determine the bit value.
Traditionally, the middle three samples of the 16 samples are used. Two UARTs can
communicate using a system like this if parameters, such as the parity scheme and
character length, are the same for both the transmitter and receiver.
When data is not transmitted in the UART protocol, a continuous stream of ones (called the
idle condition) is transmitted. Since the start bit is always a zero, the receiver can detect
when real data is once again present on the line. UART specifies an all-zeros character
called a break, which is used to abort a character transfer sequence.
Many different protocols have been defined using asynchronous characters, but the most
popular of these is the RS-232 standard, which specifies baud rates, handshaking protocols,
and mechanical/electrical details. Another popular standard using the same character
format is RS-485, which defines a balanced line system allowing longer cables than RS-232
links. Synchronous protocols are sometimes defined to run over asynchronous links. Other
protocols like Profibus extend the UART protocol to include LAN-oriented features such as
token passing.
8x, 16x, OR 32x
UART TCLK
UART TXDx
START
BIT
Freescale Semiconductor, Inc.
Figure 16-72. UART Character Format
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MPC823 REFERENCE MANUAL
5, 6, 7, OR 8 DATA BITS WITH THE
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LEAST-SIGNIFICANT BIT FIRST
ADDR
OPTIONAL
BIT
(CLOCK NOT TO SCALE)
PAR
BIT
9/16 TO 2
STOP BITS
MOTOROLA