MC68HC708XL36 FREESCALE [Freescale Semiconductor, Inc], MC68HC708XL36 Datasheet - Page 252

• Manufacturer Part Number: MC68HC708XL36
• Description: HCMOS Microcontroller Unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

SCI
Framing Errors
Baud Rate
Tolerance
MC68HC708XL36
252
To verify a stop bit and to detect noise, recovery logic takes samples at
RT8, RT9, and RT10.
samples.
If the data recovery logic does not detect a logic 1 where the stop bit
should be in an incoming character, it sets the framing error bit, FE, in
SCS1. A break character also sets the FE bit because a break character
has no stop bit. The FE bit is set at the same time that the SCRF bit is
set.
A transmitting device may be operating at a baud rate below or above
the receiver baud rate. Accumulated bit time misalignment can cause
one of the three stop bit data samples to fall outside the actual stop bit.
Then a noise error occurs. If more than one of the samples is outside the
stop bit, a framing error occurs. In most applications, the baud rate
tolerance is much more than the degree of misalignment that is likely to
occur.
As the receiver samples an incoming character, it resynchronizes the RT
clock on any valid falling edge within the character. Resynchronization
within characters corrects misalignments between transmitter bit times
and receiver bit times.
Freescale Semiconductor, Inc.
RT8, RT9, and RT10 Samples
For More Information On This Product,
Go to: www.freescale.com
000
001
010
011
100
101
110
111
Table 7. Stop Bit Recovery
Table 7
SCI
summarizes the results of the stop bit
Framing Error Flag
1
1
1
0
1
0
0
0
Noise Flag
MOTOROLA
0
1
1
1
1
1
1
0
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