Points

Points may be 1-bit, corresponding to discrete inputs, outputs, internal/memory coils, flags etc, or multi-bit (up to 32-bit), corresponding to analog inputs, outputs, integer or floating point registers etc. For each point, there is exactly one module which is allowed to change it, to ensure that processing takes place in an orderly fashion.

Points are defined in the PLC section of the config.

Example

For instance, in the basic demo, there are the following points:

L1, L2, L3, L4

the four "lights", which are changed by the chaser program;

left, right

the left and right "buttons", which are changed by the kbd module and used by the chaser program to control the direction of movement; and

quit

the quit "button", which is also changed by the kbd module; the plcshutdown module reads it so that it knows when to shut everything down.

The declaration in the config file looks like this:

point L1        "light 1" Chaser
point L2        "light 2" Chaser
point L3        "light 3" Chaser
point L4        "light 4" Chaser
point left      "<- (key L)" Kbd
point right     "-> (key R)" Kbd
point quit      "quit (key Q)" Kbd

All of the points are also displayed on the screen, by the vitrine module. No special access configuration needs to be done to allow this - any module may read any point it wishes; it's only changing them that's restricted.

In the modbus demo, the L1, L2, L3 and L4 points are also sent to the Modbus slave.

$Date: 2003/10/13 15:30:26 $