NeXT ROM Mac Address editting under Mac OS X

The MAC address for NeXT networking is contained in the ROM file. The available ROM revisions for download will not contain a unique MAC address. If you only have a single NeXT this shouldn't be a problem. If you want to network multiple Nexts you need to be sure they have unique addresses. Further, some software is locked to the MAC address. In this case it is important to have the proper MAC address to validate the software.

Step 1) Download the proper ROM for your machine

Step 2) Download a HEX editor

Step 3) Open the ROM in a HEX editor. Pictured below the MAC address (Red box) is matched between the ROM monitor and the hex editor. Use the Find and Replace fields to change the address to the desired value. Note the syntax, where a single value in the MAC address is always preceeded by a '0'. We are not quite done. You will need to calculate the CRC32 value for this part of the ROM. The CRC value is calculated using the HEX string starting with byte 0 and ending right before the start of the CRC value.

HEX editor

Step 4) Launch a TCL shell. You will need to load the CRC32 package. Then we will define the HEX string as binary (the default is ASCII which will not work).  Finally we calculate the CRC32 value and output as HEX.
Step 5) Search and replace the old with the new CRC value. You can verify the ROM for completeness using the previous emulator. After you have confirmed it will boot, it is now safe to program the real ROM chip.