Link Type - Comm Trigger

Note: This link type is available only in RMC100 CPU firmware version 20010123 and later.

This link type is used to synchronize execution of the step table with changes made externally from the PLC or other controlling system (called master below). This link type pauses the step-sequence execution until the master indicates it is ready by changing the Link Value or Extended Link Value. This function is useful when the master updates information in the RMC each machine cycle.

The RMC maintains an internal Extended Link Value for each axis; each is initialized on RMC power-up to 0. When the CommTrig (C) link type is encountered, the Link Value is compared with the Extended Link Value for the axis running the event sequence:

• If they are equal: No action is taken; the event sequence will continue to wait for a difference.

• If they are not equal: The Link Value will be copied into the Extended Link Value for the axis running the event sequence, and the link will be taken to the step indicated by the Link Next field.

There are two ways to trigger this link type to proceed:

• Change the Extended Link Value: This can be done by issuing a Set Extended Link Value (l) command. When this value is changed, the link type will reset it back to the Link Value, so it is possible to trigger using the same value each time, as long as it is different from the Link Value.

• Change the Link Value: This can be done by writing directly to the event step's Link Value field from the master. When this value is changed, the link type copies it into the Extended Link Value, so a new value must be written to the Link Value each time.

Note: The Extended Link Value is also used by the Skew Detection (<) link type. Care must be taken to ensure that these link types are not used on the same axis.

Note: Because the Extended Link Value powers up with 0, starting with a Comm Trigger (C) link value of 0 will cause the event sequence to wait the first time it encounters this link type.

Example:

This example is an axis making two moves. Suppose the PLC wants to control these moves by downloading the step sequence to the RMC. Here is how this can be done:

• The RMC starts this sequence running on axis 0. That axis will first encounter the CommTrig (C) link type and wait until the Extended Link Value or Link Value change, since both are zero.

• The PLC waits until the axis is not running either step 11 or 12.

• The PLC downloads values to these two steps. These values can include, but are not limited to, accelerations, speeds, and positions.

• The PLC issues a Set Extended Link Value command with a command value of 1 to axis 0. Alternatively, the PLC could change the Link Value in the event step table itself, but it would need to write a different value each time.

• The CommTrig (C) link type sees that the Extended Link Value differs from the Link Value of 0, so it copies the Link Value of 0 into the Extended Link Value and jumps to step 11.

• Steps 11 and 12 are executed normally.

• When step 10 is reached, the event sequence pauses again, waiting for the PLC to re-trigger the sequence.

Using with the Link Type and Link Value Dialog Box

1. Under Link Type Category, select System-wide (Basic, non-axis).

2. Under Link Type, select Comm Trigger.

3. Under Link Condition, enter the Sync Value you wish to start with.

4. Click OK.

Using without the Link Type and Link Value Dialog Box

1. Enter a 'C' into the Link Type field.

2. Enter the Link Value.

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