S912XEG128J2VAL
| Model | S912XEG128J2VAL |
| Description | IC,MICROCONTROLLER,16-BIT,CPU12 CPU,CMOS,QFP,112PIN,PLASTIC |
| PDF file | Total 1327 pages (File size: 7M) |
| Chip Manufacturer | ROCHESTER |
Chapter 20 Serial Communication Interface (S12SCIV5)
indicating that the received byte can be read. If the receive interrupt enable bit, RIE, in SCI control
register 2 (SCICR2) is also set, the RDRF flag generates an RDRF interrupt request.
20.4.6.3
Data Sampling
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 (see
Figure 20-21)
is re-synchronized:
• After every start bit
• After the receiver detects a data bit change from logic 1 to logic 0 (after the majority of data bit
samples at RT8, RT9, and RT10 returns a valid logic 1 and the majority of the next RT8, RT9, and
RT10 samples returns a valid logic 0)
To locate the start bit, data recovery logic does an asynchronous search for a logic 0 preceded by three logic
1s.When the falling edge of a possible start bit occurs, the RT clock begins to count to 16.
Start Bit
RXD
Samples
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
LSB
Start Bit
Qualification
Start Bit
Verification
Data
Sampling
RT Clock
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT2
RT3
RT4
RT5
RT6
RT7
RT8
RT9
RT1
RT2
RT3
RT10
RT11
RT12
RT13
RT14
RT15
RT CLock Count
Reset RT Clock
RT16
RT4
Figure 20-21. Receiver Data Sampling
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7.
Figure 20-17
summarizes the results of the start bit verification samples.
Table 20-17. Start Bit Verification
RT3, RT5, and RT7 Samples
000
001
010
011
100
101
110
111
Start Bit Verification
Yes
Yes
Yes
No
Yes
No
No
No
Noise Flag
0
1
1
0
1
0
0
0
If start bit verification is not successful, the RT clock is reset and a new search for a start bit begins.
MC9S12XE-Family Reference Manual , Rev. 1.19
748
Freescale Semiconductor
Because of an order from the United States International Trade Commission, BGA-packaged product lines and part numbers indicated here currently are not
available from Freescale for import or sale in the United States prior to September 2010: S12XE products in 208 MAPBGA packages
