MOTOROLA
Chapter 23. SCC UART Mode
23-1
Chapter 23
SCC UART Mode
230
230
The universal asynchronous receiver transmitter (UART) protocol is commonly used to
send low-speed data between devices. The term asynchronous is used because it is not
necessary to send clocking information along with the data being sent. UART links are
typically 38400 baud or less and are character-based. Asynchronous links are used to
connect terminals with other devices. Even where synchronous communications are
required, the UART is often used as a local port to run board debugger software. The
character format of the UART protocol is shown in Figure 23-1.
Figure 23-1. UART Character Format
Because the transmitter and receiver operate asynchronously, there is no need to connect
the transmit and receive clocks. Instead, the receiver oversamples the incoming data stream
(usually by a factor of 16) and uses some of these samples to determine the bit value.
Traditionally, the middle 3 of the 16 samples are used. Two UARTs can communicate using
this system if the transmitter and receiver use the same parameters, such as the parity
scheme and character length.
When data is not sent, a continuous stream of ones is sent (idle condition). Because the start
bit is always a zero, the receiver can detect when real data is once again on the line. UART
speciÞes an all-zeros break character, which ends a character transfer sequence.
The most popular protocol that uses asynchronous characters is the RS-232 standard, which
speciÞes baud rates, handshaking protocols, and mechanical/electrical details. Another
popular format is RS-485, which deÞnes a balanced line system allowing longer cables than
RS-232 links. Even synchronous protocols like HDLC are sometimes deÞned to run over
asynchronous links. The ProÞbus standard extends UART protocol to include
LAN-oriented features such as token passing.
UART TCLK
UART TXD
8x, 16x, or 32x
Start
Bit
Addr
Bit
Parity
Bit
(Optional)
5, 6, 7, or 8 Data Bits with the
Least SigniÞcant Bit First
9/16 to 2
Stop Bits
NOTE:
1. Clock is not to scale.
Summary of Contents for MPC860 PowerQUICC
Page 3: ...MPC860UM AD 07 98 REV 1 MPC860 PowerQUICC ª UserÕs Manual ...
Page 36: ...xxxvi MPC860 PowerQUICC UserÕs Manual MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 88: ...1 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 114: ...3 16 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 226: ...8 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
Page 262: ...9 36 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
Page 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
Page 320: ...12 12 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
Page 326: ...IV vi MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 352: ...13 26 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 394: ...14 42 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 426: ...15 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 530: ...17 26 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 632: ...21 44 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 660: ...22 28 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 708: ...24 24 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 748: ...27 20 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 846: ...31 20 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 914: ...35 12 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 948: ...36 34 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 998: ...37 48 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part VI Debug and Test ...
Page 1016: ...A 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1024: ...B 8 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1030: ...C 6 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1086: ...Glossary 12 MPC860 PowerQUICC UserÕs Manual MOTOROLA ...
Page 1106: ......