User manual

Publication 1760-UM001A-EN-P
Drawing a Circuit Diagram with Pico 4-45
How Does the Shift Register Work?
The shift pulse is switched on for exactly one cycle. To do this, the shift pulse is
generated by evaluating the change from I1 “off” to I1 “on” - the rising edge. This
allows the shift register to only shift once regardless of how long I1 remains true.
When I1 is switched on for the first time, marker relay contact M7 is off and the
break contact is closed during the first pass through the program. Thus, the series
circuit consisting of I1, break contact M7 (closed) and M8 is turned on. Although
M7 is switched on, this does not yet affect contact M7.
The contact of M8 (make contact) was still open during the first scan so a shift
pulse is not yet generated. When the relay coil M8 is activated, Pico transfers the
result to the contacts.
In the second scan, break contact M7 opens. The series circuit is now open. The
contact M8 is switched on from the result of the first scan. Now, all the storage
positions are either set or reset in accordance with the series circuit.
If the relay coils were activated, Pico transfers the result to the contacts. M8 is now
open once more. No new pulse can be generated until I1 is opened, since M7 is
open for as long as I1 is closed. This is known as a “One-shot” pulse.
How does the value reach the shift register?
When shift pulse M8 = “on”, the state of I2 (value) is transferred to storage position
M1. If I2 is switched on, M1 is set. If I2 is switched off, M1 is cleared via break
contact I2.
How is the result shifted?
Pico activates the coils in accordance with the circuit connection and its result,
from top to bottom. M4 assumes the value of M3 (value 0 or 1) before M3 assumes
the value of M2. M3 assumes the value of M2, M2 the value of M1 and M1 the
value of I2.
Why are the values not constantly overwritten?
In this example, the coils are controlled only by the “S” and “R” functions, i.e. the
values are retained in on or off states even though the coil is not constantly
switched on. The state of the coil changes only if the circuit connection up to the
coil is enabled. In this circuit, the marker relay is therefore either set or reset.
The circuit connections of the coils (storage positions) are only enabled via M8 for
one cycle. The result of activating the coils is stored in Pico until a new pulse
changes the state of the coils.
How are all the storage positions cleared?
When I3 is turned on, all the “R” coils of storage positions M1 to M4 are reset, i.e.
the coils are turned off. Since the reset was entered at the end of the circuit
diagram, the reset function has priority over the set function.