Table of Contents
Advertisement
15.7.7.1 Definition of Terms
Bit-time
Start bit
Stop bit
Frame
Data frame
Idle frame
Break frame
15.7.7.2 Serial Formats
All data frames must have a start bit and at least one stop bit. Receiving and transmitting
devices must use the same data frame format. The SCI provides hardware support for both
10-bit and 11-bit frames. The M bit in SCCxR1 specifies the number of bits per frame.
The most common data frame format for NRZ (non-return to zero) serial interfaces is one
start bit, eight data bits (Lsb first), and one stop bit (ten bits total). The most common 11-bit
data frame contains one start bit, eight data bits, a parity or control bit, and one stop bit.
Ten-bit and 11-bit frames are shown in Table 15-29.
Start
1
1
1
Start
1
1
1
1
The MSB data bit can also serve as a second STOP bit. By setting this bit permanently to one, communication with
other SCIs requiring two STOP bits could be accommodated.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
The time required to transmit or receive one bit of data, which is
equal to one cycle of the baud frequency.
One bit-time of logic zero that indicates the beginning of a data
frame. A start bit must begin with a one-to-zero transition and be
preceded by at least three receive time samples of logic one.
One bit-time of logic one that indicates the end of a data frame.
A complete unit of serial information. The SCI can use 10-bit or
11-bit frames.
A start bit, a specified number of data or information bits, and at least
one stop bit.
A frame that consists of consecutive ones. An idle frame has no start
bit.
A frame that consists of consecutive zeros. A break frame has no stop
bits.
Table 15-29. Serial Frame Formats
10-bit Frames
Data
Parity/Control
7
—
7
1
8
—
11-Bit Frames
Data
Parity/Control
8
—
8
1
9
—
Chapter 15. Queued Serial Multi-Channel Module
Serial Communication Interface
SCCxR1 Bits
STOP
M
2
0
1
0
1
0
SCCxR1 Bits
STOP
M
1
1
2
1
1
1
1
PE
0
1
0
PE
1
1
0
15-55
Advertisement
Table of Contents
