Field PG M3 BIOS Upgrade: Creating Bootable FreeDOS USB Drive

Overview: Field PG M3 BIOS Update Workflow

The SIMATIC Field PG M3 is Siemens' ruggedized industrial programming device for STEP 7 V5.x, STEP 7 Professional, TIA Portal, and S7-PLCSIM. Like any PC-class hardware, the Field PG M3 carries an AMI/Phoenix-compatible BIOS (or UEFI firmware on later sub-revisions) that occasionally requires an update to support new STEP 7/TIA Portal versions, newer Intel microcode, additional boot devices, or ACPI/battery-charge corrections on systems where the internal backup battery has been replaced.

Siemens ships each BIOS package as a self-extracting archive containing a DOS executable (commonly PHLASH16.EXE, BIOS_UPD.EXE, or MakeUSB.exe), the binary ROM image (.ROM, .WPH, or .FD), and a Update.txt with release notes. Because flashing must occur below the operating system to guarantee exclusive access to the SPI flash chip, Siemens mandates a FreeDOS boot environment. Windows cannot run the flash utility directly; even administrator rights will fail because the chipset is locked once Windows initializes ACPI.

The official Siemens procedure documented in support entry Entry ID 109758232 – IPC & Field PG firmware update process calls for the helper package Create_FREEDOS_USB_FD.zip and a Windows tool MakeUSB.exe. In practice, MakeUSB.exe refuses to detect any USB stick that does not already contain a FreeDOS boot sector, and the helper ZIP is increasingly hard to locate on Siemens' support pages. This article documents the field-proven workaround using Rufus to build the bootable FreeDOS medium, then walks through the full BIOS flashing procedure and post-update verification on a Field PG M3.

Prerequisites and Required Files

• BIOS package: Download the matching Field PG M3 BIOS update ZIP from Siemens Industry Online Support. Verify the model code (typically 6ES7710-1xxxxx or 6ES7711-1xxxxx) against the file's Update.txt before extracting.
• USB stick: 512 MB minimum, 8 GB maximum recommended. Larger sticks trigger UEFI/Legacy GPT conflicts on older Field PG revisions. SanDisk Cruzer Fit and Kingston DataTraveler 100 G3 are field-verified. Back up any data on the stick; it will be repartitioned.
• Rufus: Version 3.22 or later (4.x also supported) from rufus.ie. Rufus is portable and does not require installation.
• FreeDOS 1.3 base files: Optional. Rufus can pull the FreeDOS kernel automatically; if you need an offline path, fetch the FreeDOS USB Lite installer from freedos.org/download.
• AC power: Field PG must be connected to the charger throughout. Loss of mains during flash bricks the EC/KBC chip and forces SPI programmer recovery.
• Battery: If the BIOS update is being performed after a CMOS/RTC battery swap, install the new battery before flashing; some Field PG M3 BIOS images refuse to write if RTC_POWER_OK is low.

Why FreeDOS and Why Not Windows

The flash utility (PHLASH16 or its OEM equivalent) writes directly to the SPI NOR that holds the BIOS image, the ME (Management Engine) region, and the EC firmware. Windows locks the SPI controller's write-protect register via the chipset's SPI Protection Register (SPR) as soon as the OS enumerates ACPI. Even signed drivers cannot bypass this lock without a kernel-mode helper that the OS blocks on Secure Boot-enabled industrial images.

FreeDOS runs in real mode with no memory manager, no HAL, and no ACPI. The chipset boots in legacy mode with the SPI bus fully open for read/write. Because FreeDOS does not initialize USB 3.0 XHCI controllers, the USB stick must be plugged into a USB 2.0 port on the Field PG M3 — typically the two ports on the left side of the unit, marked with the USB trident and a non-SS label.

The MakeUSB.exe Limitation and Root Cause

MakeUSB.exe is a thin wrapper around format /FS:FAT32 /V:FREEDOS and xcopy. It scans removable drives via WMI Win32_DiskDrive and looks for a partition signature of 0x55AA plus a FREEDOS volume label. If the volume label is missing or the MBR is generic, the tool returns the error "Could not find a FreeDOS bootable USB stick. Please prepare the medium first."

On Windows 10 1903 and later, Microsoft changed the default removable-drive behaviour: format writes a Windows-style MBR (with the BOOTMGR marker) rather than a DOS-style MBR, and the volume label is upper-cased to FREEDOS only if the user explicitly types it. MakeUSB.exe was last revised for Windows 7 and is no longer maintained, so it rejects what is, in practice, a perfectly bootable FreeDOS stick.

The recommended workaround is to bypass MakeUSB.exe entirely and use Rufus as the FreeDOS medium preparer. Rufus produces a clean FreeDOS MBR, copies a known-good kernel (KERNEL.SYS), COMMAND.COM, and the FDCONFIG.SYS stub, and labels the volume FDRESIZE or FREEDOS depending on the version selected.

Building the Bootable FreeDOS USB with Rufus

1. Insert the USB stick into the programming workstation (not the Field PG M3 yet). Windows will offer to format it; cancel — Rufus handles that.
2. Launch rufus-3.xx.exe as Administrator. Confirm UAC.
3. Set the parameters exactly as in the table below.

4. Click START. Rufus downloads FD13-FullUSB.zip (~32 MB) on first use; subsequent runs use a cached copy. Acknowledge the data-loss warning.
5. When Rufus reports READY, close it. Verify the stick in Windows Explorer: the volume label must read FREEDOS and the root must contain COMMAND.COM, KERNEL.SYS, and FDCONFIG.SYS.
6. Open the Siemens BIOS update archive and copy all extracted files (preserving the directory tree) to the root of the USB stick. Typical contents: PHLASH16.EXE, BIOS.WPH, Update.txt, and a platform-specific platform.ini.
7. (Optional) Create a AUTOEXEC.BAT on the stick containing PHLASH16.EXE /S /C /D /F /P /K /R BIOS.WPH if your Update.txt documents this flag set. This allows unattended flashing once FreeDOS boots.
8. Safely eject the USB stick from the workstation.

Alternative FreeDOS USB Creation Methods

If Rufus is unavailable or blocked by corporate policy, three additional paths are documented and field-verified on Field PG M3.

• UNetbootin (legacy versions 700 and earlier): Choose Distribution → FreeDOS, select the target drive, click OK. Newer UNetbootin releases dropped FreeDOS; pin to the 700 build if you go this route.
• FreeDOS USB Lite installer from freedos.org/download: Run the installer on Windows, point it at the USB stick, and accept the default layout. Produces a FDRESIZE-labelled volume that MakeUSB.exe also accepts.
• Manual FDISK + SYS: Boot a Windows 98 SE rescue disk in a VM, run FDISK /MBR, create a primary partition, set it active, then FORMAT /S /Q X:. Copy the FreeDOS base files from the ISO. This is the slowest path and only recommended when Rufus and UNetbootin are both unavailable.

All three alternatives must end with a USB stick that contains COMMAND.COM, KERNEL.SYS, an MBR with 0x55AA, and (ideally) a FREEDOS volume label. Test by booting any legacy PC from the stick before taking it to the Field PG M3.

Executing the BIOS Update on Field PG M3

1. Shut down Windows on the Field PG M3 completely. Sleep and hibernate are not sufficient — the SPI bus is partially active and the flash utility will refuse to start.
2. Plug the prepared USB stick into a USB 2.0 port on the Field PG M3 (left side, non-SS port).
3. Power on and immediately press F2 to enter BIOS Setup. If the prompt is missed, power-cycle and retry. The Field PG M3 does not have a fast-boot option by default.
4. In the Boot tab, set Boot Option #1 to the USB stick (typically listed as UEFI: SanDisk Cruzer Fit or USB: Kingston DT100). Disable Secure Boot if it is greyed out. Press F10 to save and exit.
5. The system reboots and FreeDOS should print its banner. If you see Missing operating system or the system falls back to Windows, the USB stick is not being detected — re-check the port (USB 2.0) and the MBR.
6. At the C:\> prompt, type dir and confirm that PHLASH16.EXE and BIOS.WPH are present.
7. Run the flash utility. The most common invocation on Field PG M3 is:
   PHLASH16.EXE /S /C /D /F /P /K BIOS.WPH

Flag glossary (defaults shown in parentheses):

8. The flash typically completes in 60–90 seconds. Do not power off the unit; the utility performs a final verification pass and reports Flash complete or hex error codes (see troubleshooting matrix).
9. If /C was specified, the system reboots and re-enters Setup with defaults cleared — re-enter date/time and boot order.

Verification and Post-Update Checks

1. Power on and press F2 to enter BIOS Setup. Record the new BIOS version from the Main screen; it must match the version listed in the Siemens Update.txt.
2. Confirm boot order is still correct: Windows Boot Manager first, network boot disabled unless required for SIMATIC commissioning.
3. Boot into Windows. Open Device Manager → System Devices → Intel Management Engine Interface. Verify the ME version under Properties → Driver → Driver Version reflects the new release.
4. Run Siemens SIMATIC Field PG M3 Diagnostic Tool (if installed) and confirm that all hardware self-tests pass.
5. Launch STEP 7 / TIA Portal and verify the Field PG M3 is detected under Online → Accessible Nodes. New BIOS versions occasionally change the PG/PC interface MAC address; re-authorize the device in the project tree if STEP 7 reports an unknown MAC.
6. Check the charging profile: if the BIOS update was performed after a battery swap, the battery must charge to >80% within 90 minutes and report Healthy in the Windows Battery Report (powercfg /batteryreport). Field reports indicate that after a successful BIOS refresh, the previously stuck battery-state machine initializes correctly.

Troubleshooting Matrix

Frequently Asked Questions