RX610 Group
22. I
2
C Bus Interface (RIIC)
R01UH0032EJ0120 Rev.1.20
Page 746 of 1006
Feb 20, 2013
22.6
Digital Noise-Filter Circuits
The states of the SCLn and SDAn pins are conveyed to the internal circuitry through analog noise-filter and digital
noise-filter circuits. Figure 22.22 is a block diagram of the digital noise-filter circuit.
The on-chip digital noise-filter circuit of the RIIC consists of four flip-flop circuit stages connected in series and a
match-detection circuit.
The number of effective stages in the digital noise filter is selected by the NF[1:0] bits in ICMR3. The selected number
of effective stages determines the noise-filtering capability as a period from one to four PCLK cycles.
The input signal to the SCLn pin (or SDAn pin) is sampled on falling edges of the PCLK signal. When the input signal
level matches the output level of the number of effective flip-flop circuit stages as selected by the NF[1:0] bits in ICMR3,
the signal level is conveyed to the subsequent stage. If the signal levels do not match, the previous value is retained.
If the ratio between the frequency of the internal operating clock (PCLK) and the transfer rate is small (e.g. data transfer
at 400 kbps with PCLK = 4 MHz), the characteristics of the digital noise filter may lead to the elimination of needed
signals as noise. In such cases, it is possible to disable the digital noise-filter circuit (by clearing the NFE bit in ICFER)
and use only the analog noise-filter circuit.
Mismatch
Match
D
Q
CLK
D
Q
CLK
D
Q
CLK
D
Q
CLK
NFE
SCLn/SDAn
input signal
PCLK
NF[1:0]
Compa-
rator
D
Q
CLK
D
Q
CLK
Four-stage digital noise filter
SCLn/SDAn
internal signal
PCLK
[Legend]
NFE: Digital noise filter circuit enable bit
NF[1:0]: Digital noise filter stage selection bits
Figure 22.22 Block Diagram of Digital Noise Filter Circuit
Summary of Contents for RX600 Series
Page 1006: ...RX610 Group R01UH0032EJ0120 ...