====== MPINO STUDIO 2 Phase 2 · Understand Memory ======

This page explains the differences between **P, M, D, C, T, and R memory**, address notation, memory-region settings, where memory is used in a project, and special-bit memory.

{{ :en-us_products:mpino_studio2:memory-learning-path.svg?1000 |Memory understanding sequence }}

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

===== 1. PLC Memory Basics =====

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.

{{ :en-us_products:mpino_studio2:memory-overview.svg?1000 |Comparison of the P M D C T and R memory regions }}

^ Region ^ Unit ^ Storage form ^ Value range ^
| ''P'' | BIT | Digital input or output state on the board | 0 or 1 |
| ''M'' | BIT | Internal BIT memory | 0 or 1 |
| ''D'' | WORD | Signed internal WORD memory | -32,768 to 32,767 |
| ''C'' | WORD | Counter value (signed internal WORD memory) | -32,768 to 32,767 |
| ''T'' | WORD | Current timer value (signed internal WORD memory) | -32,768 to 32,767 |
| ''R'' | Floating Point (32 bits) | Internal Floating Point memory (real-number memory) | Approximately -3.4028235E38 to +3.4028235E38 |

==== Sharing Memory Between Arduino Code and Ladder Logic ====

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.

{{ :en-us_products:mpino_studio2:memory-sharing.svg?1000 |Arduino code and ladder logic sharing the same PLC memory }}

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]''

<code cpp>
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.
}
</code>

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.

===== 2. Memory Regions =====

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'')

{{ :products:mpino_studio2:memory-settings-modal.png?430 |Figure 1. Memory Region Settings showing the address counts and estimated SRAM use }}

^ Region ^ Default count ^ Default address range ^
| ''P'' | 64 | ''P0'' to ''P63'' |
| ''M'' | 1,024 | ''M0'' to ''M1023'' |
| ''D'' | 200 | ''D0'' to ''D199'' |
| ''C'' | 100 | ''C0'' to ''C99'' |
| ''T'' | 128 | ''T0'' to ''T127'' |
| ''R'' | 50 | ''R0'' to ''R49'' |

**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''.

==== C Region and Board Pin Mapping ====

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**.

{{ :en-us_products:mpino_studio2:memory-c-map-8a4r-s.svg?1000 |C memory and board pin mapping on MPINO-8A4R(T)-S }}

^ C address ^ Board function ^ MCU pin ^
| ''C0'' to ''C5'' | Analog inputs | ''A0'' to ''A5'' |
| ''C6'' to ''C7'' | NTC temperature inputs | ''A6'' to ''A7'' |
| ''C8'' to ''C10'' | PWM outputs | ''D21'' to ''D23'' |
| ''C11'' to ''C99'' | Remaining C region not directly assigned above | Confirm the intended use before selecting an address |

> **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, check **Settings → Ladder Pin Map Settings** and **Settings → Used Memory**.

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

===== 3. Data Types =====

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

{{ :en-us_products:mpino_studio2:memory-widths.svg?1000 |BIT BYTE WORD and DWORD sizes and ranges }}

^ Width ^ Size ^ Signed range ^ Typical use ^
| BIT | 1 bit | 0 or 1 | Contacts, coils, and ON/OFF states |
| BYTE | 8 bits | -128 to 127 | Small integers |
| WORD | 16 bits | -32,768 to 32,767 | General integers and the basic values of D, C, and T |
| DWORD | 32 bits | -2,147,483,648 to 2,147,483,647 | Large integers beyond the WORD range |

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.

===== 4. Read Memory Addresses =====

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

{{ :en-us_products:mpino_studio2:memory-addressing.svg?1000 |The M0, D0, D0.1, and WM1.2 memory address formats }}

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

==== Memory Structure ====

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

{{ :en-us_products:mpino_studio2:memory-structure.svg?1000 |How P and M bits and D C and T WORDs combine into BYTE WORD and DWORD views }}

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''.

===== 5. Find Memory Used by the Project =====

Select **Settings → Used Memory**, or press ''Ctrl+Shift+L''.

{{ :products:mpino_studio2:memory-map-modal.png?800 |Figure 2. Addresses and references in Used Memory }}

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

===== 6. Special-Bit Memory =====

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

^ Format ^ Operation ^ Example ^
| ''@ON'' | Always ON | Keeps a bit contact true |
| ''@OFF'' | Always OFF | Keeps a bit contact false |
| ''@<ms>'' | Turns ON for one scan once each specified time boundary | ''@100'' is ON for one scan every 100 ms |
| ''@F<ms>'' | Repeats ON for the specified duration, then OFF for the same duration | ''@F1000'' repeats 1 second ON and 1 second OFF |

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

{{ :en-us_products:mpino_studio2:special-memory-timing.svg?1000 |Timing comparison of @100 and @F1000 special-bit memory }}

''@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.

{{ :products:mpino_studio2:special-relay-example.png?420 |Figure 3. Special-bit memory entered in a ladder cell }}

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.

===== Troubleshooting =====

^ Symptom ^ What to check ^
| An entered address is rejected. | Check the region letter, address range, B/W/D prefix support, and ''.n'' bit-access support. |
| Memory Region Settings cannot be saved. | Check whether estimated SRAM use exceeds total SRAM and is shown in red. |
| An address does not appear in Used Memory. | Select the correct region tab and ladder/code filters, enter the address, and press ''Enter''. |
| A C counter value is unexpected. | First check for overlap with the ''C0'' through ''C10'' board pin mapping on MPINO-8A4R(T)-S. |
| ''@F1000'' cannot be entered. | Confirm that the selected cell is a bit contact and that no parentheses are present. |

===== Related Documentation =====

  * [[en-us_products:mpino_studio2:activity_bar|Phase 8 · Activity Bar and Side Panels]]

  * [[en-us_products:mpino_studio2:menus_settings|Phase 7 · Menus and Preferences]]

  * [[en-us_products:mpino_studio2:monitoring|Phase 6 · Serial and Ladder Monitoring]]

  * [[:en-us_products:mpino_studio2:first_project|Phase 1 · Create Your First Project]]
  * [[:en-us_products:mpino_studio2|MPINO STUDIO 2 User Manual]]

[[:en-us_products:mpino_studio2:first_project|← Phase 1 · Create Your First Project]] | [[:en-us_products:mpino_studio2|Back to the MPINO STUDIO 2 User Manual]]