uPD789871 Subseries 8-Bit Single-Chip Microcontrollers PUM

6.4 Operation of 8-Bit Remote Control Timer
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CHAPTER 6 8-BIT REMOTE CONTROL TIMER
The 8-bit remote control timer operates as a pulse width measuring circuit.
The width of a high-level or low-level external pulse input to the TI pin is measured by operating the 8-bit timer
counter 50 (TM50) in the free-running mode.
Noise with short pulse width can be detected since the detection of the valid edge is sampled every 2 cycles of
the count clock selected by TCL51 and TCL52, and the capture operation is not performed until the valid level has
been detected two times. Therefore, the pulse width input to the TI pin must be 5 or more of the count clock set by
TCL51 and TCL52, regardless of whether the level is high or low. If the pulse width is less than 5 clocks, it cannot
be detected, and the capture operation is not performed.
The value of timer register 50 (TM50) being counted is loaded to and retained in the capture registers (CP50 and
CP51) in synchronization with the valid edge of the pulse input to the TI pin, as shown in Figure 6-3.
Figure 6-3 shows the timing of pulse width measurement.
Figure 6-3. Pulse Width Measurement Timing (1/2)
(1) To measure pulse width in synchronization with rising edge
Count value
of TM50
INTTM50
Remark t0 = (D1 – D0) × 1/fCOUNT
D0
0H
Count starts Capture Capture
TCE50 = 1
TI
CP50
INTTM52
t1 = (100H – D1 + D2) × 1/fCOUNT
FFH
fCOUNT: Count clock frequency set by TCL51 and TCL52
D1
Preliminary User’s Manual U14938EJ1V0UM
FFH
00H D0 D1 D2 D3
t0 t1
D2
D3
Capture Capture