This is an old revision of the document!
LN has observed (not sure if always true: “cmos…yamaha part starts with a 3 (nmos parts start with 2)”
"A quick lesson in yamaha datecodes: (not sure if the cutoff was 1989, 1990 or 1991 but its one of those) Pre cutoff: yl ww LL r Post cutoff: Yyww LLlr Y = year most significant (9 or 0 or 1 for 199x or 200x or 201x) y = year least significant (2 = 1982, 3 = 1983 ... etc ... 9 = 1989) (0 = 1990 for only chips pre-cutoff?) LLl = lot code/batch code? ww = week within year r = die revision"