once in awhile you MIGHT see the Accumulator go slightly higher than the Preset ... that's because the actual "timer" (the location in the data table) is only "serviced" or "updated" by the processor when the TON "instruction" (in the ladder program) is executed ... so ... sometimes if the scan time is just a little bit too long - the processor MIGHT add just a little bit too much time to the Accumulator - and so the Accumulator MIGHT go just a little bit past the Preset ... in rare situations this "overshoot" effect can cause something like a scaling-type math operation to self-destruct - but USUALLY there's no harm done ...
but to answer your specific question: YES, the TON timer's Done bit will have a "1" status whenever the Accumulator is GREATER THAN or EQUAL TO the Preset ...
but to answer your specific question: YES, the TON timer's Done bit will have a "1" status whenever the Accumulator is GREATER THAN or EQUAL TO the Preset ...