AN2577 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

AN2577

Application note Using the eTPU angle clock

STMicroelectronics 

eTPU angle clock hardware

AN2577

2.4

Zero count synchronization

For continuous synchronization of the angle clock with the position of the wheel, the angle

clock has a feature to zero the TCR2 count on detection of a software designated edge. To

use the automatic synchronization feature of the angle clock, the zero count must coincide

with a physical tooth edge.

After the last tooth before the zero count synchronization, the software sets the LAST bit in

the TPR to indicate that the current tooth is the last one in the count cycle. Then, when the

next tooth is detected, the TCR2 count will automatically reset to 0 if the angle clock is in the

Normal or Halt mode. If the angle clock is in the High Rate mode when a tooth is detected

with the LAST bit set, the angle clock will continue the count of the ticks until it is complete

before resetting the TCR2. When TCR2 is reset by a tooth edge with LAST set, the action

also clears the LAST bit.

When the application uses the zero count synchronization feature to reset the TCR2 counter

on a designated tooth each revolution, the TCR2 counter will continuously maintain a value

proportional to the angle of the wheel over a 360 degree range. At steady state, if the

software is properly implemented, the ticks between the teeth will be accurate within about

one TCR1 count. Under deceleration, the tick positions may be in error, but the tooth angles

will be accurate, while under acceleration, the tooth positions may be delayed while the tick

count catches up at a high count rate.

If the software sets the LAST bit on alternate revolutions of the wheel, the TCR2 counter will

count over an angle range of 720 degrees before resetting to zero. This is an important

feature for 4-cycle automotive applications, where the control cycle is 720 degrees.

2.5

Note:

Error recovery

The eTPU angle clock hardware provides no automatic means to detect errors in the tooth

count while tracking the wheel angle. If missing teeth are programmed between two

normally spaced teeth, the hardware will absolutely insert the required counts, likely going

into High Rate mode for a significant portion of the count. If no missing teeth are inserted in

a gap, the counter will count no higher than TICKS counts and then go into Halt mode for the

rest of the gap. If LAST is asserted on the wrong tooth, the TCR2 counter will reset,

regardless of the TCR2 count, when the next tooth is detected. If the angle clock is

untracked by missed detection of a tooth or spurious additional tooth, it is incumbent on the

software, either in the host or the eTPU, to detect the error and initiate corrective action.

The angle clock hardware does provide means to make a correction in the TCR2 count

when an error is verified by the software. If the application determines that the angle clock

has missed a tooth count and is running with a one tooth deficit in the count, the eTPU

software can insert an additional tooth by asserting the IPH bit in the TPR. When this signal

is asserted, the hardware reacts exactly as if a physical tooth was detected. If the tick

counter is counting in normal mode, it switches to high rate mode, completes the current tick

count, then counts the inserted tooth and continues in normal mode. If the angle clock is in

halt mode, it counts the inserted tooth and starts a tick count in normal mode. Note that if

the IPH is asserted in High Rate mode, it is ignored.

Inserting a tooth by asserting IPH will increase the TCR2 count by exactly one tooth angle

by counting forward to the new angle. No counts are skipped.

If the application determines that the angle clock is ahead of the wheel, it can slow the count

by asserting the HOLD bit in the TPR. When this signal is asserted, the angle clock

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