MPC555
/
MPC556
QUEUED SERIAL MULTI-CHANNEL MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
14-51
• Break frame — A frame that consists of consecutive zeros. A break frame has no
stop bits.
14.8.7.2 Serial Formats
All data frames must have a start bit and at least one stop bit. Receiving and transmit-
ting devices must use the same data frame format. The SCI provides hardware sup-
port 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 com-
mon 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
14.8.7.3 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 IMB clock by
a modulus counter. Writing a value of zero to SCxBR[12:0] disables the baud rate gen-
erator. The baud rate is calculated as follows:
or
where SCxBR is in the range {1, 2, 3, ..., 8191}.
Table 14-28 Serial Frame Formats
10-bit Frames
Start
Data
Parity/Control
Stop
1
7
—
2
1
7
1
1
1
8
—
1
11-bit Frames
Start
Data
Parity/Control
Stop
1
7
1
2
1
8
1
1
SCI Baud Rate
f
SYS
32
SCxBR
×
-------------------------
=
SCxBR
f
SYS
32
SCI Baud Rate Desired
×
-------------------------------------------------------
=
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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