Industrial Engineer · phase 4 of 16
Retentive Memory
Memory configured to preserve selected values through a power cycle or operating-mode change.
The Explain card
- Plain English
- Retentive memory keeps its value through a power cycle. When the controller comes back, the tag is exactly what it was when the lights went out.
- Example
- A production count and the current recipe number are retentive. The line loses power at two in the morning and starts the day with the same count and the same recipe.
- Why it matters
- Whether a value survives an outage is a decision, and the wrong default bites in both directions. A retained step number can restart a sequence mid stroke, and a lost totalizer means a shift's production is gone.
- Hook
- Remembers where it was when the power went out.
Where it sits in the deck
Phase 4: PLC Memory, Tags, and Instructions
The data a program moves and the instructions that move it, from a single true or false value up to a structured array.
