DSP56303 datasheet(205/292 Pages) FREESCALE

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Operating Modes

DSP56303 User’s Manual, Rev. 2

Freescale Semiconductor

9-13

9.3.2.2 Measurement Input Period (Mode 5)

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.

Figure 9-12. Pulse Width Measurement Mode, TRM = 0

Bit Settings

Mode Characteristics

TC3

TC2

TC1

TC0

Mode

Name

Function

TIO

Clock

Input period

Measurement

Input

Internal

Mode 4 (internal clock): TRM = 1

N = write preload

M = write compare

Clock

(CLK/2 or prescale CLK)

TLR

TCR

Counter

first event

N + 1

Interrupt Service

reads TCR for

NOTE: If INV = 1, a 1-to-0 edge on TIO loads the counter, and a 0-to-1 edge on TIO

TCF (Compare Interrupt if TCIE = 1)

TIO pin

width being measured

stops the counter and loads TCR with the count.

accumulated width

of M - N clock periods.

Next 0-to-1 edge

on TIO starts

counter from current

count and process

repeats. Overflow

may occur (TOF = 1).

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