Motorola DSP56301 user manual Measurement Capture Mode, Mode 6 internal clock TRM =, Internal

Operating Modes

9.3.2.3 Measurement Capture (Mode 6)

	Bit Settings					Mode Characteristics
TC3	TC2	TC1	TC0	Mode	Name		Function	TIO	Clock
0	1	1	0	6	Capture		Measurement	Input	Internal

In Mode 6, the timer counts the number of clocks that elapse between when the timer starts and when an external signal is received. At the first appropriate transition of the external clock detected on the TIO signal, TCSR[TCF] is set and, if the TCSR[TCIE] bit is set, a compare interrupt is generated. The counter halts. The contents of the counter are loaded into the TCR. The value of the TCR represents the delay between the setting of the TCSR[TE] bit and the detection of the first clock edge signal on the TIO signal. The value of the INV bit determines whether a high-to-low (1 to 0) or low-to-high (0 to 1) transition of the external clock signals the end of the timing period. If the INV bit is set, a high-to-low transition signals the end of the timing period. If INV is cleared, a low-to-high transition signals the end of the timing period.

Mode 6 (internal clock): TRM = 1

N = write preload		first event
M = write compare
TE
Clock
(CLK/2 or prescale CLK)
TLR	N
Counter	0	N	N + 1	M	N
TCR					M
TIO pin		delay being measured

TCF (Compare Interrupt if TCIE = 1)

Counter stops counting;N +overflow1 may occur before capture (TOF = 1)

Interrupt Service reads TCR; delay

=M - N clock periods

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

Figure 9-15.Capture Measurement Mode, TRM = 0

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