Mitsubishi’s MEDOC (MELSEC Documented Code) 24 is a DOS-based PLC programming software. It was the primary tool for programming the MELSEC F, F1, F2, and early A series PLCs (such as the A0J2, A1S, A2C, and A2N).
: Essential tools for uploading and downloading programs to FX and A Series PLCs.
The standard download process for MEDOC 24 was a ritual involving: melsec medoc 24 download better
A user named KuroKage on a Japanese BBS discovered that MEDOC 24’s executable contained a hardcoded baud rate divisor. By patching bytes at offset 0x3A7F (from 0x03 for 9600 to 0x01 for 19200), the PLC could be tricked into double-speed communication. Result: Download time for a 4K program dropped from 4 minutes to 1:50.
In 2023, a German hobbyist restored a 1989 injection molding machine with a MELSEC F2-40MR. Using the patched MEDOC 24 + SC-DOSBox + FTDI cable, he downloaded a 6.2K step program in – the original DOS machine took 5 minutes 48 seconds. His comment: “It’s not instant, but it’s better . And my ears don’t bleed from the old hard drive.” Mitsubishi’s MEDOC (MELSEC Documented Code) 24 is a
| Problem | Likely Cause | The "Better" Fix | | :--- | :--- | :--- | | "File not found MEDOC.EXE" | Corrupt download or path mismatch | Re-download from a verified source. Ensure no spaces in folder names. | | "Insufficient memory" | TSR programs (Terminate Stay Resident) | Use LOADFIX /P before the command. Or boot DOSBox with minimal config. | | "COM port not responding" | USB-serial driver lost in DOSBox | Use ser2net or a hardware USB-over-Ethernet adapter for true legacy hardware. | | "Ladder monitor freezes" | CPU cycles too high | In DOSBox, press CTRL+F11 to slow down cycles until the display stabilizes. |
: Use the arrow keys to navigate and F2 to enter the workspace. Programming : Press F5 to start inserting instructions. The standard download process for MEDOC 24 was
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