68300

Can anybody find anything wrong with the following.

Having read & re read the motorola literature & the
TPU microcode for the PMA function I now have some
doubt about certain parameters.

I am running the PMA function on channel 1, my sensor
wheel has 12 teeth with 1 additional tooth.

Initially I set Num_Of_Teeth to 11 and set
TCR2_Max_Value to 24.

TCR2 counts from 0 to 11 and the first additional
tooth causes an interupt.  The TPU subtracts the
Num_Of_Teeth
from TCR2_Value and this should be 0, if not an error
will occur.  In my interupt routine I change 
Num_Of_Teeth from 11 to 23.  TCR2 now continues to
count from 12 to 23 before the next additional tooth
occurs.

TCR2 will be reset because bank signal will be a non
zero value, again The TPU subtracts the Num_Of_Teeth 
from TCR2_Value and this should be 0, if not an error
will occur & my interupt routine changes Num_Of_Teeth
from 23 to 11.
I am assuming from my documentation that the
additional tooth does not change TCR2 but does it ?

From the literature TCR2_Max_Value is a number used to
detect conditions where the TPU has missed the
additional tooth, and therefore holds the max number
that TCR2 should count to, in my case 24. From the
motorola literature TCR2 does not count the
additional teeth but can anybody confirm this.

What I am getting is an ERROR of $80, and TCR2 exceeds
TCR2_Max_Value but continues counting.  I have changed
TCR2_Max_Value and got an ERROR of $C0.

Can anybody offer any ideas or advice as myself and
three other engineers are stumped after having spent
over thirty hours brainstorming the TPU and getting no
where fast.


                 all the best Roy





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