Logix controllers address data by tag name. The legacy PLC-5, SLC 500 and MicroLogix families use file addresses instead. Both styles are in use on real sites, so this sheet covers each and then shows how this browser editor maps them.
| Item | Syntax | Meaning |
|---|---|---|
| Controller-scoped tag | Motor_Run | A named variable that every program in the controller can use. |
| Program-scoped tag | Motor_Run | Same style of name, but visible only inside the program that owns it. |
| Bit of a whole-number tag | Status_Word.5 | Bit 5 of a DINT, counting from 0. |
| Array element | Pressures[3] | The fourth element, because arrays count from 0. |
| User-defined type member | Pump_1.Speed | A member of a structure tag. |
| Timer members | Pump_Timer.PRE .ACC .EN .TT .DN | Preset and accumulated time in milliseconds, plus enabled, timing and done bits. |
| Counter members | Part_Count.PRE .ACC .CU .CD .DN .OV .UN | Preset and count, with count-up, count-down, done, overflow and underflow bits. |
| Item | Syntax | Meaning |
|---|---|---|
| BOOL | BOOL | One bit, 0 or 1. |
| Whole numbers | SINT INT DINT LINT | 8, 16, 32 and 64-bit signed integers. DINT is the usual default. |
| Floating point | REAL | 32-bit floating point. |
| Structures | TIMER COUNTER CONTROL | Built-in structured types with named members. |
The exact tag names come from the I/O configuration in the project. Open the controller organizer and copy the names from there. The form shown is for a digital module; analog and specialty modules use other member names.
| Item | Syntax | Meaning |
|---|---|---|
| Input bit, local chassis module | Local:1:I.Data.0 | Slot 1, input data, bit 0. |
| Output bit, local chassis module | Local:2:O.Data.0 | Slot 2, output data, bit 0. |
The file numbers shown (B3, N7, T4, C5, F8) are the usual defaults. A project can add files or use other numbers, so check the data file list in your own program.
| Item | Syntax | Meaning |
|---|---|---|
| Input bit | I:1/0 | Input file, slot 1, bit 0. |
| Output bit | O:2/3 | Output file, slot 2, bit 3. |
| Binary (bit) file | B3:0/5 | File B3, word 0, bit 5. |
| Integer file | N7:0 | File N7, element 0, a 16-bit integer. |
| Timer file | T4:0 T4:0.ACC T4:0.DN | Timer element with its accumulated value and done bit. |
| Counter file | C5:0 C5:0.ACC C5:0.DN | Counter element with its count and done bit. |
| Floating-point file | F8:0 | File F8, element 0. |
| Item | Syntax | Meaning |
|---|---|---|
| Input tag | TAG START I:0/0 BOOL | Declares START on input word 0, bit 0, which the editor maps to the IEC address %I0.0. |
| Output tag | TAG LAMP O:0/0 BOOL | Declares LAMP on output word 0, bit 0, mapped to %Q0.0. |
| Internal bit | TAG TURN_ON BOOL | A BOOL with no I/O address. |
| Timer or counter instance | TAG T_PUMP TON / TAG CNT CTU | An instance; read its done output as T_PUMP.Q. |
Always confirm addresses and ranges against the manual for your exact controller and software version. Want to see these addresses used in logic? Read the Allen-Bradley instruction reference.
Logix controllers use named tags that you create, such as Motor_Run, with a data type. SLC 500 and MicroLogix controllers use fixed file addresses, such as B3:0/5, where the letter and number give the file type and position. The same logic reads very differently in the two styles.
In Logix write the timer tag, a dot and DN, for example Pump_Timer.DN. In an SLC 500 or MicroLogix write the element and the bit, for example T4:0.DN. The browser editor reads the done output as T_PUMP.Q.
Use them as a guide to the format. I/O tag names in a Logix project come from the module configuration, and file numbers in an SLC project can be changed, so always check the names in your own project.
Training material. Follow your site procedures, local electrical code and the manufacturer's instructions. Lockout/tagout and a qualified person are required for real equipment.