This page explains the differences between P, M, D, C, T, and R memory, address notation, memory-region settings, the Used Memory Map, and special-bit memory.

About screenshots: Screenshots use the Korean user interface. Button positions, icons, and keyboard shortcuts are the same.

Unlike Arduino programs, PLC programs use P, M, D, C, T, and R memory. Arduino code can allocate variables from the remaining SRAM after the PLC memory regions have been allocated.

Memory holds input states, internal conditions, calculation results, timer values, and other data while the program runs. Ladder logic and Arduino C code in MPINO Studio 2 can share and use this memory.

A basic address consists of a region letter followed by a zero-based number. For example, M10 is the eleventh address in the M region, and D0 is the first address in the D region.

Ladder logic and Arduino code use the same storage for P, M, D, C, T, and R memory. A value written on one side can be read from the same address on the other side.

In Arduino code, use the ladder address name directly or write it in array form. Both forms refer to the same memory.

• Ladder M0 ↔ Arduino code M0 or M[0]
• Ladder D0 ↔ Arduino code D0 or D[0]
• Ladder R0 ↔ Arduino code R0 or R[0]

void loop() {
  M0 = true;    // Sets the M0 bit contact in the ladder to ON.
  D0 = 120;     // Shares the D0 integer between ladder and Arduino code.
  R0 = 23.5f;   // Shares the R0 floating-point value between both sides.
 
  ladderLoop(); // Runs the ladder logic with the values stored above.
}

A value changed by ladder logic can be read in Arduino code after ladderLoop() finishes. Within one scan, read and write order follows the position of the ladderLoop() call inside loop().

I/O mapping caution: The P region and C addresses mapped to board functions are synchronized with physical I/O during a ladder scan. Before sharing these regions with Arduino code, check the address and I/O direction under Settings → Ladder Pin Map Settings.

P address caution: P addresses can be reviewed and changed in Board Pin Editing. Their I/O directions and physical terminals follow the definition of the board selected for the project.

R value error caution: Because of the limits of 32-bit floating-point arithmetic, 0.1 + 0.2 may be stored as approximately 0.30000001 instead of exactly 0.3. This characteristic must be considered on controllers that use IEEE 754 32-bit floating point.

The MPINO-8A4R(T)-S board uses these default memory counts:

You can change the number of addresses used under Settings → Memory Region Settings. (Shortcut: Ctrl + Shift + M)

Memory Region Settings: Blank P, M, D, C, T, and R fields use the board defaults. Entering a value changes the count for that project. The bottom of the dialog shows estimated SRAM use together with total SRAM.

Do not confuse a count with the last address. Numbering begins at zero, so 200 D addresses run from D0 through D199.

On MPINO-8A4R(T)-S, analog inputs, NTC temperature inputs, and PWM are connected to C0 through C10 memory.

You can change the mapped memory under Settings → Ladder Pin Map Settings.

Analog/PWM output caution: When memory is mapped to an analog or PWM output, the value at the mapped address drives that output. You therefore cannot use analogWrite-related functions for the same output in Arduino code. To use an analogWrite-related function, clear Use for that output under Settings → Ladder Pin Map Settings.

Critical check: If you choose C0 through C10 as ordinary counter addresses on this board, their data can overlap with the board functions that use the same addresses. Before assigning a counter, inspect both the pin map under Board/Memory Information and the Used Memory Map.

Mapped addresses vary by board and can also be changed by the user. Check them under Settings → Ladder Pin Map Settings.

Data width is the number of bits read or stored at one time. It determines the available value range and memory use.

The R region also uses 32 bits, but it stores a floating-point value, not a DWORD integer. Do not treat R memory as DWORD access simply because both use 32 bits.

When selecting a width, consider the largest value after calculations. A value incremented every 1 ms for one day reaches 86,400,000 and therefore exceeds the WORD range.

Read memory addresses by starting with the simplest form and adding the required elements one at a time.

1. M0: BIT address 0 in the M region.
2. D0: WORD address 0 in the D region.
3. D0.1: the second bit in the D0 WORD. Bit numbering starts at zero.
4. WM1.2: the third bit in WM1, the WORD view of the M region. It refers to the same bit as M18.

This diagram shows the memory structure for bits, bytes, words, double words, and floating-point values.

The P and M regions group individual BIT addresses in sets of 8, 16, or 32 for BYTE, WORD, and DWORD views. The lowest address is the least significant bit, so WM0.0 refers to M0, and WM1.3 refers to M19.

Each D, C, or T address is one WORD. Two consecutive WORDs form a DWORD: DD0 combines D0 and D1, while DD1 combines D2 and D3. C and T use the same rule through forms such as DC0 and DT0.

Select View → Used Memory Map, or press Ctrl+Shift+L.

Inspecting this map before reassigning an address or reducing a memory-region size helps prevent duplicate use and out-of-range references.

Special-bit memory beginning with @ is updated automatically by MPINO Studio 2. It can be used in ladder bit contacts.

@ON and @OFF are case-insensitive, so @on and @off are also valid.

@100 still produces one ON scan when the program scan crosses a 100 ms boundary without landing exactly on it. It can start an operation or increment a value at regular intervals.

@F1000 provides a repeating one-second condition without code that manually toggles a state.

Follow these input rules:

• The time unit for @<ms> and @F<ms> is milliseconds (ms).
• Do not use parentheses. Enter @F1000, not @F(1000).
• Use special-bit memory only in bit contacts.
• Do not enter it as an output-coil address.

• Phase 7 · Menus and Preferences

• Phase 6 · Serial and Ladder Monitoring

• Phase 1 · Create Your First Project
• MPINO STUDIO 2 User Manual

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