mc68hc908qb4 Freescale Semiconductor, Inc, mc68hc908qb4 Datasheet - Page 116

• Manufacturer Part Number: mc68hc908qb4
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Enhanced Serial Communications Interface (ESCI) Module
13.3.3.3 Data Sampling
The receiver samples the RxD pin at the RT clock rate. The RT clock is an internal signal with a frequency
16 times the baud rate. To adjust for baud rate mismatch, the RT clock is resynchronized at these times
(see
To locate the start bit, data recovery logic does an asynchronous search for a 0 preceded by three 1s.
When the falling edge of a possible start bit occurs, the RT clock begins to count to 16.
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7.
Table 13-1
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.
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Figure
After every start bit
After the receiver detects a data bit change from 1 to 0 (after the majority of data bit samples at
RT8, RT9, and RT10 returns a valid 1 and the majority of the next RT8, RT9, and RT10 samples
returns a valid 0)
Table 13-2
summarizes the results of the start bit verification samples.
13-6):
RT CLOCK
RT CLOCK
SAMPLES
CLOCK
RESET
STATE
RxD
summarizes the results of the data bit samples.
RT
RT3, RT5, and RT7 Samples
Figure 13-6. Receiver Data Sampling
000
001
010
011
100
101
110
111
QUALIFICATION
Table 13-1. Start Bit Verification
START BIT
MC68HC908QB8 Data Sheet, Rev. 2
VERIFICATION
START BIT
Start Bit Verification
START BIT
Yes
Yes
Yes
Yes
No
No
No
No
SAMPLING
DATA
Noise Flag
0
1
1
0
1
0
0
0
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