MC68HC08AS20 Datasheet, PDF (249/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

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 17-6 summarizes the results of the stop bit
samples.
Table 17-6. Stop Bit Recovery
RT8, RT9, and RT10
Samples
Framing
Error Flag
Noise Flag
000
1
0
001
1
1
010
1
1
011
0
1
100
1
1
101
0
1
110
0
1
111
0
0
17.4.13 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. The FE flag is set at the same time that the SCRF bit (SCS1) is
set. A break character that has no stop bit also sets the FE bit.
17.4.14 Receiver Wakeup
So that the MCU can ignore transmissions intended only for other
receivers in multiple-receiver systems, the receiver can be put into a
standby state. Setting the receiver wakeup bit, RWU (SCC2), puts the
receiver into a standby state during which receiver interrupts are
disabled.
MC68HC08AS20 — Rev. 4.1
Freescale Semiconductor
Advance Information
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