A few points:
If you check this every scan, you should never get into the high word of CTA174. That would let you treat it as one 16-bit register in length which would let you use a standard ">" comparison contact instead of the more awkward CMPD.
Also, you don't CLEAR the register if it's over 150 counts, you SUBTRACT 150 from the pulse count as b_carlton noted, and add one to the gallon count. (I'm assuming you can do arithmetic on the high-speed counter count like you can on the accumulator of a normal counter -- Hosties?). Most of the time you won't happen to check it when the count is exactly 150. Assume that on one check the count is 149 so you don't do anything. Between then and the next scan, the total reaches 160. This kind of latency is unavoidable. If you clear the counter, those 10 counts or 0.06 gallons are lost permanently. If you leave 160 - 150 = 10 in the register, they're lost for this cycle, but they still get counted in the next one. Even after accumulating 100000 gallons, the latency error doesn't accumulate; you can only be off by the amount that flowed during the last scan. Subtracting even covers for the extreme case of this issue. Let's say your scan time is so long that 1000 counts have accumulated by the time you check the counter. If you add 1 to the gallon count and clear, you've lost 5.7 gallons. With the subtraction method, you only subtract 150 and add a gallon. But...the pulse count will still be at 850! Each of the next five scans will also report a total > 150, and all those gallons will get counted, albeit a bit late.
Finally, nothing says you have to totalize only complete gallons. You can add a tenth of a gallon every time your counter exceeds 15 instead if you want.
Topic: X0 Totalizer Program Help Wanted (Read 11886 times)