Rockwell Automation 1760-xxxx Pico Controller User Manual - Manual (Page 170)

Publication 1760-UM001D-EN-P - September 2005
8-2 Inside Pico
Evaluation in the Circuit Diagram and High-Speed Counter
Functions
When using high-speed counter functions, the signal state is
continuously counted or measured regardless of the processing of the
circuit diagram. (C13, C14 high-speed up/down counters, C15, C16
frequency counters.)
How Does This Affect Creation of the Circuit Diagram?
Pico evaluates the circuit diagram in these five segments in order. You
should therefore remember two points when you create your circuit
diagrams:
• The changeover of a relay coil does not change the switching
state of an associated contact until the next cycle starts.
• Always wire forward or from top to bottom. Never work
backward.
Example: Switch One Cycle Later
This is the circuit diagram of a self-latching
circuit. If I1 and I2 are closed, the switching state
of relay coil {Q1 is “held” via contact Q1.
1st cycle: I1 and I2 are switched on. Relay {Q1
picks up.
Relay contact Q1 remains off since Pico evaluates
from left to right.
2nd cycle: The self-latching function now becomes active. Pico has
transferred the coil states to contact Q1 at the end of the first cycle.
Example: Do Not Wire Backward
This example is shown in
Create and Modify
Connections on page 4-10.
It was used to illustrate
how NOT to program.
When wiring more than three contacts in series, use one of the marker
relays.
I1-I2-------{Q1
Q1
Circuit Diagram:
Start Condition:
I1, I2 switched on
Q1 switched off
I1-Q4-I3
I2-I4-{Q2
I1-Q4-I3-{M1
I2-I4-M1-{Q2