From, INSTD – Signal connection or input

Block SymbolsLicensing group: STANDARD

Function Description
The two blocks From (signal connection) and INSTD (standard input) share the same symbol. They are used for referring to another signal, either internal or external.

In the function block library, you can only find the From block. It is converted to the INSTD block at compile time if necessary. The following rules define how the REXYGEN Compiler compiler distinguishes between the two block types:

  • If the parameter GotoTag contains the __ delimiter (two successive ’_’ characters), then the block is of the INSTD type. The part (substring) of the parameter before the delimiter (DRV in the block symbol above) is considered to be the name of an IODRV type block contained in the main file of the project. The REXYGEN Compiler compiler returns an error when such block does not exist. If the driver exists in the project, the other part of the GotoTag parameter (following the delimiter, signal in this case) is considered to be the name of a signal within the corresponding driver. This name is validated by the driver and in the case of success, an instance of the INSTD block is created. This instance collects real-time data from the driver and feeds the data into the control algorithm at each execution of the task it is included in.
  • If there is no __ delimiter in the GotoTag parameter, the block is of type From. A matching Goto block with the same GotoTag parameter and required visibility given by the TagVisibility parameter (see the Goto block description) is searched. In case it is not found, the REXYGEN Compiler compiler issues a warning and deletes the From block. Otherwise an "invisible" connection is created between the corresponding blocks. The From block is removed also in this case and thus it is not contained in the resulting control system configuration.

In the case of INSTD block, the GotoTag parameter includes the symbol of the driver <DRV> and the name of the signal <signal> of the given driver:

  • <DRV>__<signal>

E.g. the first digital input of a Modbus I/O device might be referenced by MBM__DI1. Detailed information about signal naming can be found in the user manual of the corresponding I/O driver.

Since version 2.50.5 it is possible to use placeholders in names of I/O driver signals. This is useful inside subsystems where this placeholder is replaced by the value of subsystem parameter. E.g. the flag MBM__DI<id> will refer to digital input 1, 2, 3 etc. depending on the parameter id of the subsystem the block is contained in. See the SubSystem function block for information on defining subsystem parameters.



Signal coming from I/O driver or Goto block. The type of output is determined by the type of the signal which is being referred by the GotoTag parameter.




Reference to a Goto block with the same GotoTag parameter, which should be connected with the From block or a reference to input signal of the REXYGEN I/O driver, which should provide data through the block’s output.


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