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Download R8C/3NT Group User`s Manual: Hardware
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R8C/3NT Group 17.7 17. Timer RA Pulse Period Measurement Mode In pulse period measurement mode, the pulse period of an external signal input to the TRAIO pin is measured (refer to Table 17.6 Pulse Period Measurement Mode Specifications). Figure 17.4 shows an Operating Example of Pulse Period Measurement Mode. Table 17.6 Pulse Period Measurement Mode Specifications Item Count sources Count operations Specification f1, f2, f8, fOCO, fC32, fC • Decrement • After the active edge of the measured pulse is input, the contents of the read-out buffer are retained at the first underflow of timer RA prescaler. Then timer RA reloads the contents in the reload register at the second underflow of timer RA prescaler and continues counting. Count start condition 1 (count starts) is written to the TSTART bit in the TRACR register. Count stop conditions • 0 (count stops) is written to TSTART bit in the TRACR register. • 1 (count forcibly stops) is written to the TSTOP bit in the TRACR register. Interrupt request • When timer RA underflows or reloads [timer RA interrupt]. generation timing • Rising or falling of the TRAIO input (end of measurement period) [timer RA interrupt] TRAIO pin function Measured pulse input (1) TRAO pin function Read from timer Write to timer Selectable functions Programmable I/O port The count value can be read by reading registers TRA and TRAPRE. • When registers TRAPRE and TRA are written while the count is stopped, values are written to both the reload register and counter. • When registers TRAPRE and TRA are written during the count, values are written to the reload register and counter (refer to 17.3.2 Timer Write Control during Count Operation). • Measurement period selection The measurement period of the input pulse is selected by the TEDGSEL in the TRAIOC register. • Measured pulse input pin select function P1_5, P1_7 is selected by bits TRAIOSEL0 and TRAIOSEL1 in the TRASR register. • Digital filter function Whether enabling or disabling the digital filter and the sampling frequency is selected by bits TIPF0 and TIPF1 in the TRAIOC register. Note: 1. Input a pulse with a period longer than twice the timer RA prescaler period. Input a pulse with a longer “H” and “L” width than the timer RA prescaler period. If a pulse with a shorter period is input to the TRAIO pin, the input may be ignored. R01UH0087EJ0100 Rev.1.00 Jan 25, 2011 Page 235 of 601
