Motorola DSP56301 user manual Measurement Input Period Mode, Mode 5 internal clock TRM =

Operating Modes

9.3.2.2 Measurement Input Period (Mode 5)

	Bit Settings					Mode Characteristics
TC3	TC2	TC1	TC0	Mode	Name		Function	TIO	Clock
0	1	0	1	5	Input period		Measurement	Input	Internal

In Mode 5, the timer counts the period between the reception of signal edges of the same polarity across the TIO signal. The value of the INV bit determines whether the period is measured between consecutive low-to-high (0 to 1) transitions of TIO or between consecutive high-to-low (1 to 0) transitions of TIO. If INV is set, high-to-low signal transitions are selected. If INV is cleared, low-to-high signal transitions are selected. After the first appropriate transition occurs on the TIO input signal, the counter is loaded with the TLR value. On the next signal transition of the same polarity that occurs on TIO, TCSR[TCF] is set, and a compare interrupt is generated if the TCSR[TCIE] bit is set. The contents of the counter load into the TCR. The TCR then contains the value of the time that elapsed between the two signal transitions on the TIO signal. After the second signal transition, if the TCSR[TRM] bit is set, the TCSR[TE] bit is set to clear the counter and enable the timer. The counter is repeatedly loaded and incremented until the timer is disabled. If the TCSR[TRM] bit is cleared, the counter continues to increment until it overflows.

Mode 5 (internal clock): TRM = 1		first event
N = write preload
M = write compare
TE
Clock
(CLK/2 or prescale CLK)
TLR	N
Counter	0	N	N + 1	M	N
TCR					M
TIO pin		period being measured
TCF (Compare Interrupt if TCIE = 1)

NOTE: If INV = 1, a 1-to-0 edge on TIO loads the counter, and a 0-to-1 edge on TIO loads TCR with count and the counter with N.

Counter continues counting,N +does1

not stop

Interrupt Service reads TCR; period

=M - N clock periods

Figure 9-13.Period Measurement Mode, TRM = 1

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