Signal Measurement Modes; Measurement Accuracy; Measurement Input Width (Mode 4) - Motorola DSP56305 User Manual

9.4.2

Signal Measurement Modes

The following Signal Measurement modes are provided:
• Measurement Input Width
• Measurement Input Period
• Measurement Capture
9.4.2.1

Measurement Accuracy

The external signal is synchronized with the internal clock used to increment the
counter. This synchronization process can cause the number of clocks measured for the
selected signal value to vary from the actual signal value by plus or minus one counter
clock cycle.
9.4.2.2

Measurement Input Width (Mode 4)

Bit Settings
TC3 TC2 TC1
0 1 0
In this mode, the timer counts the number of clocks that occur between opposite edges of
an input signal.
Set the TE bit to clear the counter and enable the timer. After the first appropriate
transition (as determined by the INV bit) occurs on the TIO input signal, the counter is
loaded with the TLR value on the first timer clock signal received either from the
DSP56305 clock divided by two (CLK/2) or from the prescaler clock input. Each
subsequent clock signal increments the counter.
In this mode the TIO signal acts as a gating signal for the internal timer clock. The TIO
polarity depends on the INV bit value. If the INV bit is set, the timer starts on the first
high-to-low (1 to 0) signal transition on the TIO signal. If the INV bit is cleared, the timer
starts on the first low-to-high (0 to 1) transition on the TIO signal.
When the first transition of opposite polarity to the INV bit occurs on the TIO signal, the
counter stops. The TCF bit in the TCSR is set, and if the TCIE bit is set, a compare
interrupt is generated. The value of the counter (which measures the width of the TIO
pulse) is loaded into the TCR. The TCR can be read to determine the external signal
pulse width. If the TRM bit is set, the counter is loaded with the TLR value on the first
MOTOROLA
TC0 Mode Name
0 4 Input Width
DSP56305 User's Manual
Timer Modes of Operation
Mode Characteristics
Kind
Measurement
Timer/Event Counter
TIO Clock
Input Internal
9-23