Glossary · SR / RS
What is SR and RS flip-flops?
Two standard blocks that hold a boolean state: SR is set-dominant, RS is reset-dominant.
SR suits states that must not be lost, such as latching an alarm that occurred even briefly. RS suits states where stopping must win, such as a run command.
The practical question is always: if both inputs arrive in the same scan, which should win? The answer picks the block.
Related terms
- Seal-in (latch)
- A pattern that keeps an output running after a momentary button press, by feeding the output back into its own start condition.
- Function block (FB)
- A unit with inputs, outputs and internal memory that persists between scans, used by declaring an instance of it.