AN2897 Freescale Semiconductor / Motorola, AN2897 Datasheet - Page 6

• Manufacturer Part Number: AN2897
• Description: Using the eTPU Angle Clock
• Manufacturer: Freescale Semiconductor / Motorola

eTPU Angle Clock Hardware
2.3
Missing Teeth
Typically a toothed wheel used in automotive applications has a series of equally spaced teeth with one or
more teeth removed to provide a reference point. The Angle Clock hardware has circuitry to insert the
tooth count for these missing teeth under control of eTPU software. One to three missing teeth can be
added automatically by programming the field MISSCNT to a non-zero value after the last tooth edge
before the gap.
When the eTPU software programs MISSCNT to a non-zero value, the tick counter proceeds as normal
until the last count of the TICKS value is reached. Then after an additional TRR period, MISSCNT is
tested, and when it is found to be non-zero, it is decremented and TCR is incremented as if a physical tooth
had been detected. The TCR continues to increment at TRR rate according to the TICKS value for the
period after the missing tooth. This process is repeated for all missing teeth. See
Figure 4
Inserted Teeth
Detected tooth edge
Angle Clock (TCR2) resets to 0
Tick bursts
MISSCNT decrements to 0
MISSCNT decrements to 1
Software write MISSCNT = 2, sets LAST
Figure 4. Missing Teeth
The Angle Clock remains in Normal mode throughout the missing tooth count unless a new physical tooth
is detected before the final tick is counted. In that event the Angle Clock goes into High Rate mode and
completes the accelerated cycle as described above.
Using the eTPU Angle Clock, Rev. 0
6
Freescale Semiconductor