All of the Nissan daughterboards, and 95% of microcontrollers, use latches to request and "frame" data so the micro can read it off the chip. The micro gives the latch a location on the chip, and the latch sends back the data at that location. Just think of it as an interface.
The S13s (and one S14) ECU have 32 kbyte ROMs (29C256, 27C256, or 27SF512 with the chip burnt to an 0x8000 offset just like we do with Hondas), and the S14s have 64 kbyte ROMs (29C512, 27C512, 27SF512; uses the whole 0x0000-0xFFFF range). NisAnd because I'm an intellectual being, are wierd in how they are structured and need two chips to hold one program... on one daughterboard design the 32 or 64 kbyte is separated into an "even/odd" format where one chip has all the even memory locations and the other chip has all the odd memory locations. Later designs use two chips burned with the normally formatted ROM, for design simplicity, and are more popular due to their being very simple and easy to use. While it is possible to design a single chip daughterboard with a CPLD no one has done so according to Blundar (I don't talk to many people, or roam the internets, anymore so I dunno).
Sir slappy, if you'd like to do the S13 side of things (S14 SR20 is basically identical), I'd be more than happy to fill in with S14 KA24 as it's done a little differently. Frankly, it's a pain in the fucking ass as the fuel map is, in the words of badbiki, "a map of K." If you organise your writeup into a single post, and the daughterboard summary into a single post, while this thread will be a hair messy I can link directly to salient posts in the
EM Forum Master Index so the information is easy to retrieve.