Here’s how we get from a key press to the HP-65 (or emulator) actually doing something … <\/p>\n
The HP-65 key press routine is part of the wait loop. After all, that is the main thing it is waiting for.<\/p>\n
As you know, the wait loop starts at 00726. After a few instructions it gets to 00623 which checks the s0 flag to see if a key has been pressed. If not, it continues to 00452 and then through the rest of the loop. However, if s0 is 1 then we get to 00625 and start processing a key press.<\/p>\n
The first thing it does is wait a bit. 00625-00627 simply loops 16 times. It starts with P=12 and adds 1 each time until P gets back to 12.<\/p>\n
00630 clears the “a key has been pressed” flag (the s0 value that got us to here).<\/p>\n
00710 turns off the display and puts a 0 in a[0] as a starting point for what comes later.<\/p>\n
00715 puts us in the 01000 address space and causes us to execute a 01316 “key -> rom” instruction just after that. In effect we now do a “switch statement” to 01000 + the scan code of the pressed key. See below:<\/p>\n
\r\n00726 if s9 = 0\r\n00727 goto 00622\r\n00622 12 -> p ; P= 12\r\n00623 if s0 = 0\r\n00624 goto 00452\r\n00625 p + 1 -> p ; P= 13\r\n00626 if p # 12\r\n00627 goto 00625\r\n; P= 14, 15, 0, 1, 2, ..., 11\r\n00625 p + 1 -> p ; P= 12\r\n00626 if p # 12\r\n00627 goto 00625\r\n00630 0 -> s0 ; S= ............\r\n00631 if s10 = 0\r\n00632 goto 00641\r\n00641 if s5 = 0\r\n00642 goto 00734\r\n00734 if s8 = 0\r\n00735 goto 00710\r\n00710 jsb 00675\r\n.00675 12 -> p\r\n.00676 1 -> f3\r\n.00677 dispoff\r\n.00700 c <-> m ; C= 00000000000221 M =00000000000000\r\n.00701 shiftl a[w] ; A= 00000000009990\r\n.00702 return\r\n00711 1 -> f7\r\n00712 if s3 = 0\r\n00713 goto 00715\r\n00715 rom 2\r\n01316 key -> rom\r\n<\/pre>\n