Mitsubishi M70/M700 Training Lesson 2: Creating a New Program and Writing Your First Program

📷 IMAGE AREA — Entering a new program number (O1000) on the Mitsubishi M70 EDIT screen
Suggested alt text: Creating a new program number on the Mitsubishi M70 EDIT mode screen

In this lesson we learn to switch to EDIT mode on the Mitsubishi M70 control, create a new program number, write a program line, use the EOB key and check that the program is saved. In this section we will not run the program; we will only create a new one.

1. Safety before starting

While writing a new program the axes normally do not move; but if the mode is accidentally switched to MDI, AUTO or MEMORY, commands can be executed. So first make sure the machine is not running, the spindle is stopped, do not press CYCLE START, set the mode switch to EDIT, and check that there is no running or half-finished program. The Mitsubishi manual recommends checking the program and compensation values and dry-running the program before moving to actual machining.

2. What is EDIT mode?

EDIT mode is used to make changes to a program: creating a new program, writing a line, correcting a wrong line, inserting/deleting a line, changing the program name/number and deleting a program. EDIT mode is not used to run a program; running is done later in AUTO or MEMORY mode.

3. Steps to create a new program

Key names may vary slightly by builder, but the basic sequence is the same. Step 1 – Switch to EDIT mode: set the mode switch to EDIT; you should see EDIT at the top/status line. If EDIT is not shown, do not start writing. Step 2 – Open the program editing screen: open the EDIT (or PROGRAM on some panels) menu; at the bottom you may see EDIT, FILE, SEARCH, PROGRAM, INPUT, INSERT, DELETE menus (names vary by panel version). Step 3 – Decide the new program number: each program gets a separate number, e.g. O1000. The first character is the letter O, not zero. On some machines typing only 1000 is enough; the control may show it automatically as O1000. Step 4 – Enter the program number: type O1000 and, depending on the panel, press INPUT (or EOB/INSERT). In most M70 applications the new program number is entered and INPUT is pressed; when accepted, an empty editing screen opens.

4. What if the program already exists?

If a program numbered O1000 was already created, a new empty program does not open. The control may open the existing O1000, warn that the program already exists, or prevent creating a new program with the same number. The Mitsubishi programming manual states that main programs and subprograms must not use the same number; using the same number can cause an input error. In that case open the program list, check whether O1000 exists; if it will be used, open the existing program, and if a new program is needed, choose a different number (e.g. O1001). Do not delete an existing program without checking it.

5. Points to consider when choosing a program number

The program number should be assigned to the shop’s scheme. Example scheme: O1000 test program, O1100 part 1, O1200 part 2, O2000 mold program, O9000 special/protected program. Some ranges like O8000 and O9000 may have been used by the machine builder as special macros, tool change, measurement or service programs. So it is safer for beginners to use normal numbers like O1000, O1001, O1100, O1200 where possible. Do not change protected programs.

6. Writing the first program line

After the new program is opened, lines can be written. As an example let us create a simple program with no motion — it will not machine a real part, it is only to learn the logic of writing a program:

O1000
N10 G21
N20 G17 G90
N30 M30

7. What is the EOB key?

EOB is the abbreviation of End of Block. After a CNC line is written, pressing the EOB key tells the control that the line is finished. On screen EOB is usually shown by the ; mark (e.g. N10 G21;). The operator usually does not type a semicolon directly from the keyboard; instead the EOB key on the panel is pressed. The Mitsubishi manual explains that lines end with an EOB code and this is shown on screen by the ; mark.

8. Let us write the lines step by step

Line 1: type N10 G21 → EOB → INPUT/INSERT. The screen should show N10 G21;. G21 tells the program to work in the metric (millimeter) system. Line 2: N20 G17 G90 → EOB → INPUT/INSERT. Screen: N20 G17 G90;. G17 selects the X-Y plane, G90 the absolute dimension system. Line 3: N30 M30 → EOB → INPUT/INSERT. Screen: N30 M30;. M30 is the general program-end command that ends the program and returns it to the start.

9. The resulting program and N numbers

On the program screen you should generally see:

O1000
N10 G21;
N20 G17 G90;
N30 M30;

Some M70 controls also add an EOB after the program number (O1000;); some show the number separately as a header. Both views depend on the panel implementation. Are N numbers mandatory? No; the program O1000 / G21 / G17 G90 / M30 also runs. But N numbers are useful in training: finding lines is easier, errors are found more easily, and Program Restart and starting from a specific line become more orderly. Numbering lines as N10, N20, N30, N40 in steps of 10 makes it easier to insert a line later (e.g. N25 between N20 and N30).

10. If a line is written wrong (ALTER/change)

For example we accidentally wrote N20 G18 G90;; the correct one should be N20 G17 G90;. General correction sequence: move the cursor onto the wrong line → rewrite the correct line (N20 G17 G90) → EOB → ALTER (change) key. On some M70 panels CHANGE, REPLACE or INPUT is used instead of ALTER; this replaces the existing line with the new one. Whether the Undo feature is available in program editing may depend on a control parameter; the M700 Handbook states that the Undo function can be enabled with a user parameter.

11. Inserting a new line (INSERT)

To insert a new line between two lines: move the cursor to the insertion point → type the new line → EOB → INSERT. For example to insert N25 G40 G49 G80; between N20 G17 G90; and N30 M30;, the line is written and INSERT is pressed; the result:

N20 G17 G90;
N25 G40 G49 G80;
N30 M30;

12. Deleting a line (DELETE)

Line deletion is usually: move the cursor onto the line to delete → DELETE → confirm if the control asks. On some panels only a specific command in the line can be deleted (e.g. only G17 from N20 G17 G90;); in that case pay attention to which word the cursor is on. Deleting the whole program and deleting only one line are not the same; deleting the entire program is covered in a separate lesson.

13. How is the program saved?

On the Mitsubishi M70 control, programs opened in NC memory are usually written to memory automatically after each entered line; so unlike on a computer, you may not need to keep pressing SAVE. Still, it should be checked: exit the program or return to the program list, search for O1000 in the list, reopen the program and check that the lines you wrote are present. If the list shows O1000 and the lines remain when reopened, the program is saved to memory. The M700 Handbook states that if Cycle Start is given during a file write or delete, automatic operation is blocked.

14. Why is a program end needed? (M30 / M99)

At the end of a program M30 is usually used (e.g. N100 M30;). M30 ends the program, stops automatic operation and returns the program to the start position. If there is no M30 at the end, the program may stop on the last line, may not return to the start as expected, or behave differently by control implementation; so a program-end command must be present in main programs. In subprograms, M99 is usually used. We will move to main programs and subprograms later.

15. Simple training program (summary)

Let us see what we learned in one program — safer for training since there is no axis motion (still, we do not run it in this lesson):

O1000
N10 G21;
N20 G17 G90;
N30 G40 G49 G80;
N40 M30;

16. Common mistakes when creating a program

• Writing zero instead of the letter O: Wrong 01000, correct O1000.
• Not pressing EOB: if the line is not ended, the control may not accept it or may merge it with the next command; use EOB after every line.
• Using the same program number: if O1000 exists it cannot be created a second time; check the list first.
• Being in AUTO instead of EDIT: EDIT must be selected for writing/editing.
• Changing the wrong line: before ALTER/DELETE, check that the cursor is on the correct line.
• Forgetting to write M30: a program-end command must be at the end of the main program.
• Trying to open a protected program: the O8000/O9000 ranges especially must be used carefully.

17. Application steps

A beginner operator should work in this order: (1) Set the mode to EDIT. (2) Open the program editing screen. (3) Type the new program number: O1000. (4) Press INPUT. (5) Type the first line: N10 G21. (6) Press EOB. (7) Press INSERT/INPUT. (8) Enter the other lines the same way. (9) Write M30 at the end. (10) Check O1000 from the program list. (11) Reopen the program to verify the lines are saved.

18. Lesson summary

In this lesson we switched to EDIT mode; created a new program number; learned that the O number is the program number; organized lines with N numbers; ended lines with EOB; learned the logic of INPUT, INSERT and ALTER; ended the program with M30; and checked that the program is in NC memory.

Next lesson — Lesson 3: Finding, calling and resetting a program in NC memory (opening the program list, searching by O number, activating the selected program and bringing it to the start before running).

📷 IMAGE AREA — Writing, inserting, changing and deleting lines with the EOB, INSERT, ALTER and DELETE keys
Suggested alt text: Mitsubishi M70 program editing with EOB insert alter delete keys