JSONMaker_V2 UDFB for Rockwell Micro850 (ST)

Overview

JSONMaker_V2 is a User Defined Function Block (UDFB) written in Structured Text for Rockwell Micro850 PLCs. It concatenates an input array of strings into a single JSON-formatted string, using custom keys from the InputNames array if provided, or falls back to keys "A" through "T" for up to 20 elements. Only non-empty strings are included in the output JSON.

Features

• Accepts an input array of up to 20 strings (InArray), each up to 32 characters.
• Accepts an optional array of up to 20 string keys (InputNames), each up to 32 characters.
• Outputs a JSON string (JsonString) with keys from InputNames if provided, otherwise uses "A" to "T".
• Skips empty strings in the input array.
• Designed for use in Connected Components Workbench (CCW) with Micro850 PLCs.
• Controlled by enable (FBEN) and done (FBENO) flags.

Function Block Interface

Input Array

• InArray : ARRAY[0..19] OF STRING[32]
  The array of strings to be concatenated into JSON.
• InputNames : ARRAY[0..19] OF STRING[32]
  Optional array of key names for each input. If blank, the key defaults to "A"-"T".
• FBEN : BOOL
  Set to TRUE to enable execution of the function block.

Output JSON

• JsonString : STRING[255]
  The resulting JSON string.
• FBENO : BOOL
  Set to TRUE when the function block has completed execution.

Function Block Variables


How It Works

1. When FBEN is set to TRUE, the function block starts execution.
2. It initializes the output string as a JSON object ({").
3. It loops through each element of InArray (indices 0 to 19):
   • If the string is not empty, it adds a key-value pair to the JSON string.
   • The key is taken from InputNames[i] if not blank, otherwise it is a letter from "A" (index 0) to "T" (index 19).
   • Commas are added between entries as needed.
4. The JSON string is closed with a }.
5. FBENO is set to TRUE to indicate completion.

Example

Suppose you have the following input:

InArray[0] := 'Apple';
InArray[1] := '';
InArray[2] := 'Banana';
InArray[3] := '';
InArray[4] := 'Cherry';
InputNames[0] := 'fruit1';
InputNames[2] := '';
InputNames[4] := 'fruit3';
// ... rest are empty
FBEN := TRUE;

After execution, JsonString will be:

{"fruit1":"Apple","C":"Banana","fruit3":"Cherry"}

Usage Notes

• Only non-empty strings are included in the output JSON.
• The output string is limited to 255 characters. If the total JSON exceeds this, it will be truncated.
• The function block must be called with FBEN := TRUE to execute. FBENO will be set to TRUE when done.
• Designed for use in Micro850 PLCs with Structured Text (ST) in CCW.

License

This code is provided as-is for educational and industrial automation purposes.