Chapter 4. Ladder Diagram (LD) Programming86 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C4.3.3 Set Coil, Reset CoilSet Coil and Reset Coil with a retentive variableassignedSet Coil and Reset Coil with a non-retentivevariable assignedThe SET and RESET coils can be used to keep (i.e. latch) the state of a reference either ON or OFF.WarningSET / RESET coils write an undefined result to thetransition bit for the given reference. This result differsfrom that written by Series 90-70 CPUs and couldchange for future PACSystems CPU models.Because they write an undefined result to transitionbits, do not use SET or RESET coils with references usedon POSCON or NEGCON transition contacts.When a SET coil receives power flow, it sets its discrete reference ON. When a SET coil does notreceive power flow, it does not change the value of its discrete reference. Therefore, whether or notthe coil itself continues to receive power flow, the reference stays ON until the reference is reset byother logic, such as a RESET coil.When a RESET coil receives power flow, it resets a discrete reference to OFF. When a RESET coil doesnot receive power flow, it does not change the value of its discrete reference. Therefore, its referenceremains OFF until it is set ON by other logic, such as a SET coil.The last solved SET coil or RESET coil of a pair takes precedence.The SET and RESET coils can be assigned a retentive variable or a non-retentive variable.Valid memory areas: %I, %Q, %M, %T, %SA - %SC, and %G. Symbolic discrete variables are permitted.Bit-in-word references on any word-oriented memory except %AI, including symbolic non-discretememory, are also permitted.Example of Set Coil, Reset CoilThe coil represented by E1 is turned ON when reference E2 orE6 is ON and is turned OFF when reference E5 or E3 is ON.
