AN2577 datasheet(9/34 Pages) STMICROELECTRONICS

9 / 34 page

AN2577

eTPU angle clock hardware

9/34

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.

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.

If the angle clock completes the count of the missing teeth plus all of the inserted ticks, and

a new tooth is not detected, the angle clock goes into Halt mode as described above.

Inserted Teeth

Tick bursts

Software write MISSCNT = 2, sets LAST

MISSCNT decrements to 1

MISSCNT decrements to 0

Angle Clock (TCR2) resets to 0

Detected tooth edge

AN2577 Datasheet(PDF) 9 Page - STMicroelectronics