uPD789871 Subseries 8-Bit Single-Chip Microcontrollers PUM
uPD789871 Subseries 8-Bit Single-Chip Microcontrollers PUM
uPD789871 Subseries 8-Bit Single-Chip Microcontrollers PUM
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6.4 Operation of 8-<strong>Bit</strong> Remote Control Timer<br />
78<br />
CHAPTER 6 8-BIT REMOTE CONTROL TIMER<br />
The 8-bit remote control timer operates as a pulse width measuring circuit.<br />
The width of a high-level or low-level external pulse input to the TI pin is measured by operating the 8-bit timer<br />
counter 50 (TM50) in the free-running mode.<br />
Noise with short pulse width can be detected since the detection of the valid edge is sampled every 2 cycles of<br />
the count clock selected by TCL51 and TCL52, and the capture operation is not performed until the valid level has<br />
been detected two times. Therefore, the pulse width input to the TI pin must be 5 or more of the count clock set by<br />
TCL51 and TCL52, regardless of whether the level is high or low. If the pulse width is less than 5 clocks, it cannot<br />
be detected, and the capture operation is not performed.<br />
The value of timer register 50 (TM50) being counted is loaded to and retained in the capture registers (CP50 and<br />
CP51) in synchronization with the valid edge of the pulse input to the TI pin, as shown in Figure 6-3.<br />
Figure 6-3 shows the timing of pulse width measurement.<br />
Figure 6-3. Pulse Width Measurement Timing (1/2)<br />
(1) To measure pulse width in synchronization with rising edge<br />
Count value<br />
of TM50<br />
INTTM50<br />
Remark t0 = (D1 – D0) × 1/fCOUNT<br />
D0<br />
0H<br />
Count starts Capture Capture<br />
TCE50 = 1<br />
TI<br />
CP50<br />
INTTM52<br />
t1 = (100H – D1 + D2) × 1/fCOUNT<br />
FFH<br />
fCOUNT: Count clock frequency set by TCL51 and TCL52<br />
D1<br />
Preliminary User’s Manual U14938EJ1V0UM<br />
FFH<br />
00H D0 D1 D2 D3<br />
t0 t1<br />
D2<br />
D3<br />
Capture Capture