User manual

LD Language Elements

SR2MAN01 11/2007 99

Latch mode:

Symbol of a Discrete output, used as a coil in latch mode:

The Set coil, also called the latch coil, is energized as soon as the contacts to which

it is connected are conducting, then stays set even if later the contacts are no longer

conducting.

This behavior is identical to that of an RS logic flip-flop.

Example:

Switching a lamp on and off with two pushbuttons: See Latching Mode

below.

Unlatch mode:

Symbol of a Discrete output, used as a coil in unlatch mode:

The RESET coil, also called the unlatch coil, is deactivated when the contacts to

which it is connected are conducting. It remains inactive even if later the contacts

are no longer conducting.

Example:

Switching a lamp on and off with two pushbuttons: See Unlatch Mode

BPI1 is connected to input I1. BPI2 to input I2. The lamp is controlled by output Q1.

The lamp turns on when pushbutton BPI1 is pressed, and it turns off when

pushbutton BPI2 is pressed.

Note: Output use rule:

z An output may only be used at one single point in the program as a coil.

z If a SET coil is used for a Discrete output, it is advisable to provide a RESET coil

for this output. The RESET coil takes priority over the SET coil.

The use of a Set coil on its own is only justified for activating an alarm signal that

can be reset only by an INIT + ON action from the program.

Note: For reasons of upward compatibility for programs operating with Zelio 1

smart relays, the four types of modes for any given Q output coil or M auxiliary relay

can be used in the same wiring diagram in Zelio 2.

In this case, the operating mode is determined by the coil activated first.

SQ-

RQ-

SQ1

RQ1