How to Build a Step Sequence with Internal M Bits

A machine cycle is easier to debug when each step is an explicit state.

Represent each step as a state

Splitting a cycle into internal state bits makes the sequence easier to trace than one oversized rung.

M10 = Step 1
M11 = Step 2
M12 = Step 3

Transition pattern

X0            -> PLS M100
M100          -> SET M0 / SET M10
M10 AND X2    -> PLS M101
M101          -> SET M11 / RST M10
M11           -> T0 K20
T0            -> PLS M102
M102          -> SET M12 / RST M11
M12 AND X3    -> PLS M103
M103          -> RST M0 / RST M12

Keep outputs separate from state transitions

M0 AND M10 -> Y0
M0 AND M11 -> Y1
M0 AND M12 -> Y2

Design checks

• Prevent multiple step bits from being ON together
• Add timeout handling where a sensor may never arrive
• Define how Stop/Fault resets step state
• Define the restart step after an interruption