Karl Bernst writes: After doing a web search, I found a listing for the keyboard routine. http://www.classiccmp.org/mail-archive/classiccmp/1998-04/0779.html It appears that you enter an 3 digit octal number and then hit a function key. H - puts the number in the H register L - puts the number in the L register S - puts the number into memory pointed to by HL and then increments HL. G - Loads the program counter with the contents of HL I dug out my copy of "the 8080a Bugbook", but it does not discuss the operation of the keyboard. You might try to find the May-July 1976 issue of Radio Electronics. --Doug ========================================= Doug Coward @ home in Poulsbo, WA Analog Computer Online Museum and History Center http://dcoward.best.vwh.net/analog =========================================