Freescale Semiconductor DSP56366 - Manual (Page 246)

Timer Modes of Operation
DSP56366 24-Bit Digital Signal Processor User Manual, Rev. 4
11-16 Freescale Semiconductor
11.4.2 Signal Measurement Modes
The following signal measurement modes are provided:
• Measurement input width
• Measurement input period
• Measurement capture
These functions are available only on timer 0.
11.4.2.1 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.
11.4.2.2 Measurement Input Width (Mode 4)
In this mode, the timer 0 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. Load the timer’s count value into the TLR. After
the first appropriate transition (as determined by the INV bit) occurs on the TIO0 input pin, the counter is
loaded with the TLR value on the first timer clock signal received either from the DSP56366 clock divided
by two (CLK/2) or from the prescaler clock input. Each subsequent clock signal increments the counter.
If the INV bit is set, the timer starts on the first high-to-low (1 to 0) signal transition on the TIO0 signal.
If the INV bit is cleared, the timer starts on the first low-to-high (0 to 1) transition on the TIO0 signal.
When the first transition opposite in polarity to the INV bit setting occurs on the TIO0 signal, the counter
stops. The TCF bit in the TCSR is set and a compare interrupt is generated if the TCIE bit is set. The value
of the counter (which measures the width of the TIO0 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 timer clock received following
the next valid transition occurring on the TIO0 input pin and the count is resumed. If the TRM bit is
cleared, the counter continues to be incremented on each timer clock.
This process is repeated until the timer is disabled (i.e., TE is cleared).
If the counter overflows, the TOF bit is set, and if TOIE is set, an overflow interrupt is generated.
The counter contents can be read at any time by reading the TCR.
Bit Settings Mode Characteristics
TC3 TC2 TC1 TC0 Mode Name Kind TIO0 Clock
0 1 0 0 4 Input Width Measurement Input Internal