The Laserwriter 12/640 and the Laserwriter 16/600 have similar setup.
Here is a link to the 300 or so page manual for the 12/640
https://manuals.info.apple.com/MANUALS/0/MA728/en_US/0340211ALW12640UM.pdf
I have a 16/600 which I've always used with Appletalk, so I thought this would be a good time to see if I could get it working on TCP/IP in OSX.
After much grief, I finally got it working. The catch is that you'll need an OS9 Mac to set up the IP address on the printer. You'll need OS9 (or older), and Apple Printer Utility software. You can set the printer IP address using Apple Printer Utility.
If you don't have an old Classic OS Mac, or the old Apple Printer Utility software, then you're probably SOL.
The biggest problem I had was figuring out what IP address to use for the printer. The Apple Printer Utility software showed the printer already had an IP address, so I tried to use that address in OSX. I could set it up as an IP printer, but when I tried to print I'd get the message that the printer couldn't be found.
I finally figured out that the IP address asigned to the printer wasn't compatible with my network. To get a more appropriate address, I looked up the IP address of my computer using the the Network system preference, and checking it under Built in Ethernet. It's a set of four groups of numbers separated by periods. The trick is to use the same first three groups of numbers, but use a different number for the last group. The first three groups of numbers identify the network, and the last group of numbers identify the device. I just gave it 35 for the last number so it probably wouldn't conflict with any other devices on my network.
Then I went back to my old OS9 mac, and used the Apple Printer Utility to set the IP address for the printer to the new one.
Now back to OSX and add a printer. Select IP printer, and then Line Printer. Enter the IP address for printer. This time when I print it goes through just dandy. The only problem now is that the paper keeps jamming. A problem for another day.
