An anonymous source wrote the following back in the late '80s.
The following is description of the proceedure I used to store my BA, DO, and CO files in EPROM so they could be easily loaded after a cold start. This has been done sucessfully on both a Model 100 and a 102. It would probably work on a 200 but it has not been tested.
The basic concept that I used was to take a snapshot (memory image) of the ram after all programs that I would use had been loaded. This snapshot would be stored in the eprom so that after a cold start it could be copied back into the ram without having to reload it from cassette or disk.
Since the eprom is 32k and the ram is 32k it would not be possible to store all of the ram and still have room for a transfer program. I discovered that there are 3 major areas that have to be saved inorder to restore the computer to previous operating state. They are; an area from maxram to the end of memory, a small area just below himem, and the file area.
The first area, maxram (F5F0h) to the end of memory (FFFFh) contains all of the directory entries as well as most operating system parameters. Also in this area is a flag to indicate an option rom is present. If the name of the option rom is to appear in the directory after a cold start then this location will have to be changed. The location is F62Ah, in a Model 100 it must be set to FFh, in a Model 102 it must be set to 00h. If you have any machine language programs that have been loaded just below maxram they can be saved at the same time by moving the beginning address down to include them.
The second area that must be saved is approximately 560 bytes just below himem. The exact purpose of this area is not well documented but it has to be saved or this proceedure won't work.
The third area is the file area from the beginning of ram (8000h on a 32k machine) to the end of the last file (pointed to by the data stored at FBB2h). You should make sure that the paste buffer and any unsaved basic programs have been eliminated by doing a NEW and a CLEAR command.
Each of these areas are saved by using the SAVEM command. Although they could be saved to ram and then transferred out to the programmer it is easier to use a floppy disk and save them to it first.
The next step is to determine the size of each of the saved areas and where it will be stored in the eprom. We can then write a short transfer program to move the three segments back into there proper locations in ram. The entry point for the transfer program is 00h. Upon entry the first two things it should do are disable the interrupts, and set the stack pointer to an unused area at FCC0h. On exit we will have to jump to a short program in ram that switches back to the regular rom and does a RST 0.
There is a reserved area in the option rom (40-47h) that must have two special characters followed by a six letter filename. In a Model 100 the letters TC must be in locations 40 & 41h. In the Model 102 they must be the letters AB. On a cold start the computer will then load the six letter filename into the directory. This part is optional since the option rom can also be started by the statement CALL 63012 from basic. If you do not use the letters TC to activate the option rom it is necessary to change the option rom flag in the maxram area. If you forget the computer will cold start each time you try to activate the option rom.
After inserting the option rom and performing a cold start the menu should appear with the option rom filename right after SCHEDL. Move the cursor to the file name and press enter to jump to the option rom. If you had a basic program setup as an IPL then it will load and execute automatically.
