Question 44:
A NAND logic function may be built up from a regular AND function plus an inverter function (a NOT gate) on the output:
The same strategy of "building" a NAND gate may be done in PLC ladder-diagram programming, by combining a normally-closed contact instruction with two contacts in series.
Examine these two Allen-Bradley PLC programs, and explain why the left-hand program is "wasteful" while the right-hand program makes more efficient use of available bits:
Examine these two Siemens S7 PLC programs, and explain why the left-hand program is "wasteful" while the right-hand program makes more efficient use of available bits in the same ways the Allen-Bradley example programs were wasteful/efficient: