MC68HC08JL8 Datasheet, PDF (129/212 Pages) Freescale Semiconductor, Inc – Microcontrollers

Functional Description
To determine the value of a data bit and to detect noise, recovery logic takes samples at RT8, RT9, and
RT10. Table 9-3 summarizes the results of the data bit samples.
Table 9-3. 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.
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10. Table 9-4
summarizes the results of the stop bit samples.
Table 9-4. Stop Bit Recovery
RT8, RT9, and RT10
Samples
000
001
010
011
100
101
110
111
Framing
Error Flag
1
1
1
0
1
0
0
0
Noise Flag
0
1
1
1
1
1
1
0
9.4.3.4 Framing Errors
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.
MC68HC908JL8/JK8 • MC68HC08JL8/JK8 • MC68HC908KL8 Data Sheet, Rev. 3.1
Freescale Semiconductor
129