mc68hc908gp32 Freescale Semiconductor, Inc, mc68hc908gp32 Datasheet - Page 140

• Manufacturer Part Number: mc68hc908gp32
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Serial Communications Interface Module (SCI)
To determine the value of a data bit and to detect noise, recovery logic takes samples at RT8, RT9, and
RT10.
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10.
summarizes the results of the stop bit samples.
13.4.3.4 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.
13.4.3.5 Baud Rate Tolerance
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
140
Table 13-3
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.
summarizes the results of the data bit samples.
RT8, RT9, and RT10
RT8, RT9, and RT10
Samples
Samples
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
MC68HC908GP32 Data Sheet, Rev. 10
Table 13-4. Stop Bit Recovery
Table 13-3. Data Bit Recovery
NOTE
Determination
Error Flag
Data Bit
Framing
0
0
0
1
0
1
1
1
1
1
1
0
1
0
0
0
Noise Flag
Noise Flag
0
1
1
1
1
1
1
0
0
1
1
1
1
1
1
0
Freescale Semiconductor
Table 13-4