Delta RMC101 User Manual download pdf (Page 663)

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101

Appendix A: Command Reference

A-11

Note: This command should only be used in the Event Step table. This command does nothing

when issued directly from the PLC.

The Poll (?) command modifies the operation of most link types (exceptions are listed below).

This command can only be issued in the Event Step table and affects the link type on the same

step as the Poll command.

The Poll command is useful in applications where it is necessary to check for two or more

conditions at the same time. For instance it may be required to start a move and then wait until

the axis is in position or an error bit is set.

When a link type is encountered without this command, the sequence will wait until the condition

is true before proceeding. No other steps are run on that axis’s step sequence until the condition

is met, as shown below:

When a link type is encountered with this command, then one of two steps will be run next. If the

condition is true, then the step number indicated in the Link Next field will be run. If the condition

is false, then the next step (current step plus one) will be run. This is shown below:

When the Poll command is executed, the Command Value is stored in the Extended Link Value,

in the same way as in the Set Extended Link Value (l) command. This allows polling of link types

that require the Extended Link Value to be set. Because most link types do not use the Extended

Link Value, the Command Value can usually be left at zero (0).

Note: Only one polled link type is evaluated per control loop (1 or 2 ms).

The following link types should not be used with the Poll command:

• DelayMS (D) and DelayTicks (d) link types

These link types do not work with the Poll command because the timer or counter is restarted

each time the link type is encountered in the sequence. An alternative for controlling time in a

polled loop is to use the Timer (T and t) link types.

• InputRise (I) and InputFall (i) link types

These link types detect rising or falling edges in the current control loop. However, because a

polled loop will take more than one control loop, rising or falling edges will likely be missed. Use

the level-sensitive InputHigh (O) and InputLow (o) link types instead.

• LoopStart (#) and LoopEnd (-) link types

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