EFI firmware archive for Apple logic board 820-2883, with the suffix A, probably denoting the board revision. This number belongs to the 13-inch MacBook A1342. The 1.55 MB RAR should contain a ROM image for the board SPI flash, used to recover machines with corrupted firmware or a locked firmware state. Write it with an external programmer after saving the existing contents, and check that the chip capacity equals the image size before flashing.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @biosarchive. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
Back up your own chip before writing any dump, and match the full board number and revision. Flashing guide →