Queued Serial Multi-Channel Module
MPC561/MPC563 Reference Manual, Rev. 1.2
15-52
Freescale Semiconductor
Frame
A complete unit of serial information. The SCI can use 10-bit or 11-bit frames.
Data frame
A start bit, a specified number of data or information bits, and at least one stop bit.
Idle frame
A frame that consists of consecutive ones. An idle frame has no start bit.
Break frame
A frame that consists of consecutive zeros. A break frame has no stop bits.
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
.
15.7.7.3
Baud Clock
The SCI baud rate is programmed by writing a 13-bit value to the SCxBR field in SCI control register zero
(SCCxR0). The baud rate is derived from the MCU IMB3 clock by a modulus counter. Writing a value of
zero to SCxBR[12:0] disables the baud rate generator. The baud rate is calculated as follows:
or
Eqn. 15-4
Table 15-29. Serial Frame Formats
10-bit Frames
SCCxR1 Bits
Start
Data
Parity/Control
STOP M
PE
1
7
—
2
0
0
1
7
1
1
0
1
1
8
—
1
0
0
11-Bit Frames
SCCxR1 Bits
Start
Data
Parity/Control
STOP M
PE
1
8
—
2
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.
1
1
1
8
1
1
1
1
1
9
—
1
1
0
SCI Baud Rate
f
SYS
32
x
SCxBR
------------------------------
=
Summary of Contents for MPC561
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