CIRCC Datasheet, PDF (16/70 Pages) SMSC Corporation – Consumer Infrared Communications Controller

Receiver Bit Cell Synchronization
The Consumer IR Receiver demodulates
incoming ASK waveforms into NRZ data for the
SCE. The CIrCC uses the edges of the
demodulated incoming infrared data to indicate
changes in bit state.
For continuous periods of high or low data
without transitions, the CIrCC samples the signal
level in the center of each incoming bit period.
Using the Receiver Bit Cell Synchronization
mechanism, any transition resets the timer that is
used in the sampling process to eliminate errors
due to timing differences between the receive
decoder and the incoming bit period (Figure 7).
Receiver synchronization can be disabled to
allow direct sampling of the demodulated
incoming infrared data stream at some preset
receive bit rate. This is useful in situations where
the speed of the receive data is not strictly
known. In such cases, the receive bit rate is set
as high as possible, the Receiver Bit Cell
Synchronization is disabled, and the system
software is used to measure the bit-cell period
from the over sampled data. The learned
parameters can then be used to switch to the
synchronized, fixed bit-cell mode to reduce
processing overhead in the host CPU for all
future transactions.
Clock 1 2 3 4 5 6 7 8
9 10
Sync
Sync
IR Rx Data
NRZ Rx Data
1 1 0 00 1 11
0
(SYNC)
Clock 1 2 3 4 5 6 7 8 9 10 11
IR Rx Data
NRZ Rx Data
(No SYNC)
1 1 0 0 0 1 1110
FIGURE 7 - REMOTE CONTROL RECEIVER: SYNC VS. NO SYNC
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