Freescale Semiconductor MC68HC908MR32, MC68HC908MR16 Start Bit Verification, Data Bit Recovery

Serial Communications Interface Module (SCI)

Table 13-1. Start Bit Verification

RT3, RT5, and RT7	Start Bit	Noise Flag
Samples	Verification
000	Yes	0
001	Yes	1
010	Yes	1
011	No	0
100	Yes	1
101	No	0
110	No	0
111	No	0

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 13-2summarizes the results of the data bit samples.

Table 13-2. Data Bit Recovery

RT8, RT9, and RT10	Data Bit	Noise Flag
Samples	Determination
000	0	0
001	0	1
010	0	1
011	1	1
100	0	1
101	1	1
110	1	1
111	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 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 13-3summarizes the results of the stop bit samples.

Table 13-3. Stop Bit Recovery

	RT8, RT9, and RT10	Framing	Noise Flag
	Samples	Error 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
	MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
166				Freescale Semiconductor