HD64336900G Datasheet, PDF (229/408 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

14.3.9 Sampling Mode Register (SPMR)
SPMR controls the serial communication function.
Bit
7 to 3
Bit Name

Initial
Value
All 1
2
STDSPM 1
1, 0 
All 1
R/W Description

Reserved
These bits are always read as 1.
R/W Noise Filter Function Select
Selects the noise filter function for the RXD pin in
asynchronous mode.
0: Noise filter circuit is enabled
1: Noise filter circuit is disabled

Reserved
These bits are always read as 1.
• Noise Filter Circuit
The RXD input signal is latched through the noise filter circuit. The noise filter circuit
comprises a series of three latch circuits and a match detection circuit. The RXD input signal is
sampled by the basic clock with the 16 times the transfer clock frequency. If three latch outputs
match, its level is transferred to the next stage. If not, the circuit holds the previous value.
That is, when the incoming signal holds the same level for three clock cycles, it is regarded as
the proper signal. If the levels of the signal is less than three clock cycles, the signal is
regarded as a noise.
Sampling clock
RXD input signal
C
D
Q
Latch
C
D
Q
Latch
C
D
Q
Latch
Match
detection
circuit
SPMR
(STDSPM)
Internal RXD
signal shown
in figure 14.1
Internal basic clock cycle
Sampling clock
Figure 14.2 Block Diagram of Noise Filter Circuit
Rev. 1.00, 11/03, page 201 of 376