Tony, It's been 20+ years since I built an interface to my ELFII bus for two 4K SWTech memory boards (32x1(?) dynamic rams in white ceramic DIPs). I can't tell you specifically why SC1 is sending high signals, but back then dynamic RAMs were very common. I seem to remember that SC1 could be used for dynamic RAM refresh. I'll have to dig a bit to come up with more info - if I find it, I'll post again. -John M.