MC68HC08AS32A Datasheet, PDF (181/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
Functional Description
To verify the start bit and to detect noise, data recovery logic takes samples at RT3,
RT5, and RT7. Table 13-2 summarizes the results of the start bit verification
samples.
Table 13-2. Start Bit Verification
RT3, RT5, and RT7
Samples
000
001
010
011
100
101
110
111
Start Bit
Verification
Yes
Yes
Yes
No
Yes
No
No
No
Noise Flag
0
1
1
0
1
0
0
0
Start bit verification is not successful if any two of the three verification samples are
logic 1s. If start bit verification is not successful, the RT clock is reset and a new
search for a start bit begins.
To determine the value of a data bit and to detect noise, recovery logic takes
samples at RT8, RT9, and RT10. Table 13-3 summarizes the results of the data
bit samples.
Table 13-3. Data Bit Recovery
RT8, RT9, and RT10
Samples
000
001
010
011
100
101
110
111
Data Bit
Determination
0
0
0
1
0
1
1
1
Noise Flag
0
1
1
1
1
1
1
0
NOTE:
The RT8, RT9, and RT10 samples do not affect start bit verification. If any or all of
the RT8, RT9, and RT10 start bit samples are logic 1s following a successful start
bit verification, the noise flag (NF) is set and the receiver assumes that the bit is a
start bit.
MC68HC08AS32A — Rev. 1
MOTOROLA
Serial Communications Interface (SCI)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
181