MC68336/376
TIME PROCESSOR UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
11-8
measurement with additional transition detect function allows for a special-purpose
23-bit period measurement. It can detect the occurrence of an additional transition
(caused by an extra tooth on the sensed wheel) indicated by a period measurement
that is less than a programmable ratio of the previous period measurement.
Once detected, this condition can be counted and compared to a programmable num-
ber of additional transitions detected before TCR2 is reset to $FFFF. Alternatively, a
byte at an address specified by a channel parameter can be read and used as a flag.
A non-zero value of the flag indicates that TCR2 is to be reset to $FFFF once the next
additional transition is detected.
Refer to TPU programming note Period Measurement, Additional Transition
Detect (PMA) TPU Function (TPUPN15A/D) for more information.
11.4.7 Period Measurement with Missing Transition Detect (PMM)
Period measurement with missing transition detect allows a special-purpose 23-bit
period measurement. It detects the occurrence of a missing transition (caused by a
missing tooth on the sensed wheel), indicated by a period measurement that is greater
than a programmable ratio of the previous period measurement. Once detected, this
condition can be counted and compared to a programmable number of additional tran-
sitions detected before TCR2 is reset to $FFFF. In addition, one byte at an address
specified by a channel parameter can be read and used as a flag. A non-zero value of
the flag indicates that TCR2 is to be reset to $FFFF once the next missing transition is
detected.
Refer to TPU programming note Period Measurement, Missing Transition Detect
(PMM) TPU Function (TPUPN15B/D) for more information.
11.4.8 Position-Synchronized Pulse Generator (PSP)
Any channel of the TPU can generate an output transition or pulse, which is a projec-
tion in time based on a reference period previously calculated on another channel.
Both TCRs are used in this algorithm: TCR1 is internally clocked, and TCR2 is clocked
by a position indicator in the user's device. An example of a TCR2 clock source is a
sensor that detects special teeth on the flywheel of an automobile using PMA or PMM.
The teeth are placed at known degrees of engine rotation; hence, TCR2 is a coarse
representation of engine degrees. For example, each count represents some number
of degrees.
Up to 15 position-synchronized pulse generator function channels can operate with a
single input reference channel executing a PMA or PMM input function. The input
channel measures and stores the time period between the flywheel teeth and resets
TCR2 when the engine reaches a reference position. The output channel uses the
period calculated by the input channel to project output transitions at specific engine
degrees. Because the flywheel teeth might be 30 or more degrees apart, a fractional
multiplication operation resolves down to the desired degrees. Two modes of opera-
tion allow pulse length to be determined either by angular position or by time.