On a FANUC control, parameters, tool offsets, work zeros, macro variables, PMC parameters and part programs live in battery-backed SRAM. If the battery dies, alarm 935 (SRAM ECC) appears or the memory module is replaced, all of it can be lost. The safest way to keep a machine’s complete setup in one file is to enter the BOOT screen at power-on and take an SRAM backup. This guide follows the 0i-B and 0i-C maintenance manuals (B-63835, B-64115) and the 0i-F maintenance manual (B-64605EN); the 0i-D screen is similar to the 0i-F.
What does an SRAM backup contain, and what does it not?
| Data | In the SRAM backup? |
|---|---|
| CNC parameters | Yes |
| Tool offsets, work offsets (G54–G59), work shift | Yes |
| Part programs (those in CNC memory) | Yes |
| Macro common variables (#500 series) | Yes |
| PMC parameters (keep relays, timers, counters, data tables) | Yes |
| Pitch error compensation data | Yes |
| PMC ladder program | No; it is in flash ROM and is saved separately with SYSTEM DATA SAVE |
| CNC system software, servo software | No; system files cannot be copied |
| Programs on a data server or ATA card | No (on the 0i-F the “SRAM + ATA PROG FILE” option may include them) |
So a complete machine backup consists of two files: the SRAM backup and the PMC ladder file. Save both on the same memory card and keep it with the machine’s nameplate data.
Which memory card can be used?
The BOOT system reads the memory card in the PCMCIA slot; CF cards go in with an adapter. The card must be FAT formatted (FAT16 on the 0i-F); large cards come from a PC as FAT32 and give “MEMORY CARD IS NOT AVAILABLE” or “MOUNT ERROR”. Formatting the card with MEMORY CARD FORMAT in the BOOT menu is the surest way. If the card has a write-protect switch it must be off, otherwise “MEMORY CARD PROTECTED” appears.
How do I enter the BOOT screen?
- With the machine switched off, insert the memory card.
- Hold down the two rightmost soft keys below the screen together and switch the machine on.
- Keep them held until SYSTEM MONITOR MAIN MENU appears.
- On panels without soft keys (touch panels), hold the numeric keys 6 and 7 on the MDI keyboard together instead.
Use [UP] and [DOWN] to move, [SELECT] to enter, and confirm each action with [YES] or [NO]. Emergency stop may be pressed; the servos do not power up, which is normal.
Main menu: 0i-B/0i-C versus 0i-D/0i-F
On the 0i-B and 0i-C the menu lines are: SYSTEM DATA LOADING, SYSTEM DATA CHECK, SYSTEM DATA DELETE, SYSTEM DATA SAVE, SRAM DATA BACKUP, MEMORY CARD FILE DELETE, MEMORY CARD FORMAT and END.
On the 0i-F, END is at the top and a USER DATA LOADING line is added: END, USER DATA LOADING, SYSTEM DATA LOADING, SYSTEM DATA CHECK, SYSTEM DATA DELETE, SYSTEM DATA SAVE, SRAM DATA BACKUP, MEMORY CARD FORMAT. Selecting SRAM DATA BACKUP opens the SRAM DATA UTILITY screen, which has a third option, AUTO BKUP RESTORE (restore from the automatic backup in flash ROM).
Line numbers vary by series and software edition; follow the menu name, not the number.
Steps to take an SRAM backup
- In the main menu move to SRAM DATA BACKUP and press [SELECT].
- On the next screen choose “1. SRAM BACKUP (CNC → MEMORY CARD)”.
- Answer “BACKUP SRAM DATA OK? HIT YES OR NO” with [YES].
- If a file of the same name exists on the card you are asked to overwrite it; if you want to keep the old backup, answer [NO] and use another card.
- While “SRAM DATA WRITING TO MEMORY CARD” is shown, do not remove the card or switch off.
- When “SRAM BACKUP COMPLETE. HIT SELECT KEY” appears, press [SELECT].
- Leave BOOT with END; answer “ARE YOU SURE?” with [YES] and the machine starts normally.
File names depend on the series. On the 0i-B/0i-C the name follows the SRAM size: SRAM256A.FDB for 256 KB, SRAM0_5A.FDB for 0.5 MB, SRAM1_0A.FDB and SRAM1_0B.FDB for 1 MB (in 512 KB pieces), SRAM2_0A–D.FDB for 2 MB. On the 0i-F the name is SRAM_BAK.001; if the data does not fit on one card, “SET MEMORY CARD NO.002” asks for a second card and SRAM_BAK.002 is created. On the 0i-F make sure there is no old SRAM_BAK file on the card before backing up.
After the backup, put the card in a PC and copy the file into a folder named with the machine and date (for example VMC2_0iMC_2026-10-21); do not let a single card be the only copy.
Restoring the SRAM backup
- Insert the card holding the backup file and enter the BOOT screen.
- Select SRAM DATA BACKUP → “2. RESTORE SRAM (MEMORY CARD → CNC)”.
- Answer “RESTORE SRAM DATA OK?” with [YES] and wait for “RESTORE COMPLETE”.
- Leave with END and power the machine off and on.
Two important warnings:
- A restore replaces the whole SRAM. Offsets, programs and PMC counters entered since the backup go back to their state on the backup date.
- On machines with absolute encoders, if parameters were restored, bit 4 (APZ) of parameter 1815 must be set to 0 and the reference position re-established on every axis. Otherwise the machine zero may be shifted and the stroke limits work wrongly.
A backup belongs to the machine with the same serial number. Another machine’s SRAM backup, even of a similar model, changes axis directions, stroke limits and servo settings to suit that machine and carries a crash risk.
PMC ladder backup: SYSTEM DATA SAVE
The ladder program belongs to the machine builder and is not in the SRAM backup. To save it:
- Select SYSTEM DATA SAVE in the main menu.
- Find the file starting with PMC in the list (for example PMC-RB, PMC-SB) and press [SELECT]. System files (NC BASIC, DGB0SRVO) cannot be saved from this screen; they are protected.
- Answer “SAVE OK?” with [YES]. A file such as PMC_RB.000 is created on the card; if the name exists, the extension counts up as 001, 002 (up to 031).
- After “FILE SAVE COMPLETE”, note the saved file name.
The ladder is restored with SYSTEM DATA LOADING; a file of the same type in flash ROM is deleted first and the one on the card is written. Because this changes the machine’s logic, do it only with the same machine’s own file.
Automatic backup on the 0i-F (AUTO BKUP RESTORE)
On the 0i-F, bit 1 (ABI) of parameter 10340 enables automatic SRAM backup; the control copies SRAM to flash ROM at set intervals, and 10342 selects the number of backups kept. When SRAM is corrupted, one of the dated backups is restored with BOOT → SRAM DATA UTILITY → “3. AUTO BKUP RESTORE”. This does not replace the memory card backup; the card backup is the only copy that can be kept away from the machine.
Common BOOT error messages
| Message | Meaning and action |
|---|---|
| MEMORY CARD NOT EXIST | No card in the slot, or not fully seated. Remove and reinsert. |
| MEMORY CARD IS NOT AVAILABLE | Card type not supported. Use a card type recommended by FANUC. |
| MEMORY CARD MOUNT ERROR | Card cannot be accessed; the format may be damaged. Format it from BOOT. |
| MEMORY CARD PROTECTED | Write-protect switch is on. Switch it off. |
| MEMORY CARD FULL / CHANGE MEMORY CARD | Card is full. Delete unneeded files or insert an empty card. |
| MEMORY CARD BATTERY ALARM | The battery of an SRAM-type card is flat. Replace the card battery. |
| FILE SAVE ERROR | Writing to the card failed. Check that the card is sound and seated. |
| MAX EXTENSION OVER | The extension of a same-named file passed 031. Delete old backups from the card. |
| ILLEGAL FORMAT FILE | The selected file does not belong to this control or is damaged. Use the right machine’s file. |
| FLASH MEMORY NO SPACE | Flash ROM is full. Delete unneeded user files. |
How often should a backup be taken?
- When the machine arrives and commissioning is complete.
- Before and after every parameter change.
- Before a battery change.
- Before and after a service visit (board, drive or motor replacement).
- Regularly, at least once a year.
Write the machine name, serial number, control type, software edition (read from the SYSTEM screen) and date on the backup. In a shop with several machines, mixing up files is more dangerous than not having a backup.
Frequently asked questions
How do I back up FANUC parameters?
For a full backup, switch the machine on while holding the two rightmost soft keys and choose SRAM DATA BACKUP → SRAM BACKUP in the BOOT menu. If you only want the parameters, in normal operation SYSTEM → [PARAM] → [(OPRT)] → [PUNCH] writes them to the card or to a PC over RS-232; that file is text and can be read.
I cannot get into the BOOT screen. What should I do?
Press the keys while the machine is fully off and keep them held through the whole start-up; do not release before the screen appears. On touch or keyless screens try keys 6 and 7. Some machine builders lock access to BOOT; then the builder’s service procedure is needed.
Can I open the SRAM backup on a PC and read the parameters?
No. .FDB and SRAM_BAK files are binary memory images; they can only be restored on the same control. For a readable parameter list use the text file produced with PUNCH.
Is the SRAM backup any use after alarm 935?
Yes, that is exactly what it is for. Replace the battery first, then RESTORE SRAM from BOOT, then re-establish the reference on axes with absolute encoders. Without a backup the whole memory is cleared and the data is entered by hand.
Why does “ARE YOU SURE? HIT YES OR NO” appear at END?
Selecting END closes the BOOT system and starts the CNC normally. Answer [YES] to leave; [NO] returns to the main menu. It is an exit confirmation, not a warning.
Mentor CNC Disclaimer: This content was prepared for training purposes from the FANUC 0i-B, 0i-C and 0i-F maintenance manuals. Menu names, file names and screens vary with the control series, software edition and the machine builder’s settings. Restoring SRAM and loading a ladder change the machine’s behaviour completely; do this only with the same machine’s own backup and, where necessary, with authorised service present. Mentor CNC accepts no liability for damage arising from use of this material; the machine builder’s manual always takes precedence.