Here’s what happens when you press 123.45 EEX 78 CHS. <\/p>\n
The numbers (0-9) end up in A[0]. <\/p>\n
\r\nA[0] starts with 0 because of:\r\n00701 shiftl a[w] ; A= 00000000009990\r\n\r\npressing the 0-9 keys give:\r\nkey scan addr instr\r\n[0] (044) 01044\trom 5 ;-> 02445\r\n[1] (004) 01004\trom 5 ;-> 02405\r\n[2] (003) 01003\trom 5 ;-> 02404\r\n[3] (002) 01002\trom 5 ;-> 02403\r\n[4] (024) 01024\trom 5 ;-> 02425\r\n[5] (023) 01023\trom 5 ;-> 02424\r\n[6] (022) 01022\trom 5 ;-> 02423\r\n[7] (064) 01064\trom 5 ;-> 02465\r\n[8] (063) 01063\trom 5 ;-> 02464\r\n[9] (062) 01062\trom 5 ;-> 02463\r\n\r\nwhich leads to:\r\nd9: 02463 a + 1 -> a[x]\r\nd8: 02464 a + 1 -> a[x]\r\nd7: 02465 ... : a + 1 -> a[x]\r\nd6: 02423 a + 1 -> a[x]\r\nd5: 02424 a + 1 -> a[x]\r\nd4: 02425 ... : a + 1 -> a[x]\r\nd3: 02403 a + 1 -> a[x]\r\nd2: 02404 a + 1 -> a[x]\r\nd1: 02405 ... :\ta + 1 -> a[x]\r\nd0: 02445 goto 02506\r\n\r\nso A[0] ends with 0-9 to match the pressed key.<\/pre>\nWhat happens next with the digits is: <\/p>\n
\r\n02506 if c[m] = 0 ; if no prefix(es)\r\n02507 goto 02736\r\n; put C and M back \r\n02736 c <-> m ; C= 00000000000000 M= 00000000000221\r\n02737 if s3 = 0 ; if in RUN mode\r\n02740 goto 02511\r\n02511 rom 2\r\n01112 if s1 = 0 ; if not input_started\r\n01113 goto 01245\r\n\r\n;if the auto_enter flag is set\r\n; c -> stack\r\n;endif\r\n;clear auto_enter flag\r\n;\r\n01245 0 -> s11\r\n01246 0 -> f1 ; clear auto_enter flag\r\n01247 if s11 = 0 ; if f1 wasn't set\r\n01250 goto 01252\r\n01251 c -> stack\r\n\r\n; set B for \"\".\r\n01252 0 -> c[w]\r\n01253 12 -> p\r\n01254 c - 1 -> c[wp] ; C= 09999999999999\r\n01255 c + 1 -> c[s] ; C= 19999999999999\r\n01256 c + 1 -> c[s] ; C= 29999999999999\r\n01257 b <-> c[w] ; B= 29999999999999 C= 02009999999999\r\n; set C=0\r\n01260 0 -> c[w] ; C= 00000000000000\r\n\r\n; if . not yet pressed\r\n; move decimal point another place to the right\r\n; endif\r\n01261 if s2 = 0 ; if not dot_pressed\r\n01262 goto 01127\r\n01263 goto 01130\r\n01127 shiftr b[w] ; B= 02999999999999\r\n\r\n; \/\/ put A[0] digit in next available position\r\n; \/\/ (the next available position is determined from the mask normally in B)\r\n; for (p=0; C[p]==0; p++)\r\n; shift digit in A[0] left\r\n01130 b <-> c[w] ; B= 00000000000000 C= 02999999999999\r\n01131 c + 1 -> c[w] ; C= 03000000000000\r\n01132 0 -> p ; P= 0\r\n01133 if c[p] >= 1\r\n01134 goto 01151\r\n01135 p + 1 -> p ; P= 1\r\n01136 shiftl a[wp] ; A= 00000000009910\r\n01137 goto 01133\r\n; P= 2 A= 00000000009100\r\n; P= 3 A= 00000000001000\r\n; P= 4 A= 00000000010000\r\n; P= 5 A= 00000000100000\r\n; P= 6 A= 00000001000000\r\n; P= 7 A= 00000010000000\r\n; P= 8 A= 00000100000000\r\n; P= 9 A= 00001000000000\r\n; P=10 A= 00010000000000\r\n; P=11 A= 00100000000000\r\n; P=12 A= 01000000000000\r\n01137 goto 01133\r\n01133 if c[p] >= 1\r\n01134 goto 01151\r\n\r\n; restore mask\r\n01151 c - 1 -> c[w] ; C= 02999999999999\r\n01152 b <-> c[w] ; B= 02999999999999 C= 00000000000000 <\/pre>\nWe now have the digit(s) in the A register and the mask (B register) set. Next is: <\/p>\n
\r\n; if just started data entry (this is digit 1)\r\n01153 if p # 3\r\n01154 goto 01366\r\n01366 if s1 = 0\r\n01367 goto 01361\r\n; then\r\n01361 shiftl a[w] ; A= 10000000000000\r\n01362 1 -> s1 ; S= .1.......... (input_started)\r\n01363 goto 01156\r\n01156 shiftr a[ms] ; A= 01000000000000\r\n01157 c -> a[s]\r\n01160 if s7 = 0 ; no EEX yet\r\n01161 goto 01163\r\n01163 1 -> s9 ; S= .1.......9.. (display_input)\r\n01164 0 -> f3 ; S= .1.......9.b f= ..2..5.. (not display_x)\r\n01165 1 -> f1 ; f= .12..5.. (set auto_enter)\r\n01166 rom 1\r\n00567 a <-> c[w] ; A= 00000000000000 C= 01000000000000\r\n00570 c -> a[w] ; A= 01000000000000\r\n00571 if a[m] >= 1 ; often if a[m]=0 then a[w]=0 (ie set exp 0 too)\r\n00572 goto 00546\r\n00546 c + 1 -> c[xs] ; C= 01000000000100 (actually test xs. if 9 dont goto)\r\n00547 goto 00470\r\n00470 0 -> c[xs] ; C= 01000000000000\r\n00471 13 -> p ; P= 13\r\n00472 c - 1 -> c[x] ; C= 01000000000999\r\n00473 if b[p] = 0\r\n00474 goto 00463\r\n00463 p - 1 -> p ; P= 12\r\n00464 c + 1 -> c[x] ; C= 01000000000000\r\n00465 jsb 00473\r\n00473 if b[p] = 0\r\n00474 goto 00463\r\n00475 12 -> p\r\n00476 if a[p] >= 1\r\n00477 goto 00574\r\n00574 a <-> c[m]\r\n00575 rom 2\r\n01176 if c[xs] = 0\r\n01177 goto 01334\r\n01334 if c[m] >= 1\r\n01335 goto 01337\r\n01337 if p # 14\r\n01340 goto 01217\r\n01217 rom 1\r\n00620 if s8 = 0\r\n00621 goto 00531 <\/pre>\nThe input_started flag has been set.<\/p>\n
We have also set the display_input flag instead of the more usual display_x flag.<\/p>\n
The C register (stack X) contains the actual value (1e0) in case we decide to use it as currently keyed in (ie press a operation key).<\/p>\n
If we key in additional digits, input_started is set so we don’t initialize values like we just did. A slightly different path gets followed: <\/p>\n
\r\n; elseif this is digit 2+ (but pre . pre EEX)\r\n; A= 12000000000000 B= 02999999999999 C= 01000000000000\r\n01153 if p # 3\r\n01154 goto 01366\r\n01366 if s1 = 0 ; if not input_started\r\n01367 goto 01361\r\n; then\r\n01370 if s2 = 0 ; if not dot_pressed\r\n01371 goto 01107\r\n01107 shiftr b[wp] ; B= 00299999999999\r\n01110 jsb 01156\r\n01156 ...\r\n(as above)\r\n; S= .1.......9.b f= .12..5..\r\n; A= 01200000000000 C= 01200000000001 P= 12\r\n00621 goto 00531 <\/pre>\nPressing dot changes subsequent behaviour. It no longer pushes the decimal point to the right with each digit entered: <\/p>\n
\r\n; press [.]\r\n; key scan addr instr\r\n; [.] (043) 01043 goto 01271\r\n;\r\n; which leads to:\r\n01271 if c[m] >= 1 ; if prefix(es)\r\n01272 goto 01270\r\n01273 1 -> s2 ; S= .12......... (dot_pressed)\r\n01274 if s1 = 0 ; if not input_started\r\n01275 goto 01044\r\n01276 goto 01304 ; but it has\r\n01304 c <-> m ; C= 01230000000002 M= 00000000000221\r\n01305 shiftr a[w] ; A= 01230000000000\r\n01306 jsb 01157 ; never returns?\r\n01157 ...\r\n(as above but more looping and s2 set)\r\n; S= .12......9.b f= .12..5..\r\n; A= 01230000000000 C= 01230000000000\r\n; P= 13 C= 01230000000999\r\n; P= 12 C= 01230000000000\r\n; P= 11 C= 01230000000001\r\n; P= 10 C= 01230000000002 (C= 1.23e2 ie \"123.\")\r\n; P= 12\r\n00621 goto 00531\r\n\r\n; press [4]\r\n;\r\n; which leads to:\r\n; P=10 A= 12340000000000 B= 00029999999999 C= 01230000000002\r\n\r\n; if this is digit 2+ (but after . pre EEX)\r\n01153 if p # 3\r\n01154 goto 01366\r\n01366 if s1 = 0 ; if not input_started (not digit 1)\r\n01367 goto 01361\r\n01370 if s2 = 0 ; if not dot_pressed\r\n01371 goto 01107\r\n; then\r\n01372 p - 1 -> p ; P= 9\r\n01373 0 -> b[p] ; B= 00020999999999\r\n01374 jsb 01156\r\n01156 ...\r\n(as above)\r\n; S= .12......9.b f= .12..5..\r\n; A= 01234000000000 C= 01234000000002 P= 12\r\n00621 goto 00531<\/pre>\nThe dot_pressed (s2) flag is set.<\/p>\n
You can see the mask in B now has a “hole” (0) to the right of the decimal point digit (2). This lets the “4” show through on the display. We see ” 123.4″ because A contains “01234” and B contains “00020999999999”.<\/p>\n
More digits add more holes (0s) to the right of the decimal point in the mask (register B). eg:<\/p>\n
\r\n; press [5]\r\n;\r\n; which leads to:\r\n; P= 9 A= 12345000000000 B= 00020999999999 C= 01234000000002\r\n\r\n; if this is digit 2+ (but after . pre EEX: s2=1 s7=0)\r\n01153 if p # 3\r\n01154 goto 01366\r\n01366 if s1 = 0 ; if not input_started (not digit 1)\r\n01367 goto 01361\r\n01370 if s2 = 0 ; if not dot_pressed\r\n01371 goto 01107\r\n; then\r\n01372 p - 1 -> p ; P= 8\r\n01373 0 -> b[p] ; B= 00020099999999\r\n01374 jsb 01156\r\n01156 ...\r\n(as above)\r\n; S= .12......9.b f= .12..5..\r\n; A= 01234500000000 C= 01234500000002 P= 12\r\n00621 goto 00531 <\/pre>\nThe mask now looks like “00020099999999”. There are two “holes” in the mask to the right of the decimal point to allow the “4” and “5” to show through. We see ” 123.45″.<\/p>\n
The C register contains 1.2345e2 or 123.45<\/p>\n
Pressing EEX activates another part of the number entry microcode. It looks like: <\/p>\n
\r\n; press [EEX]\r\n; key scan addr instr\r\n; EEX (072) 01072 goto 01277\r\n;\r\n; which leads to:\r\n01277 if c[m] >= 1 ; if prefix(es)\r\n01300 goto 01047\r\n01301 1 -> s7 ; S= .12....7.... (eex_pressed)\r\n01302 if s1 = 0 ; if not input_started\r\n01303 goto 01004 ; (put a 1 in mantissa)\r\n01304 c <-> m ; C= 01234500000002 M= 00000000000221\r\n01305 shiftr a[w] ; A= 01234500000000\r\n01306 jsb 01157\r\n\r\n01157 c -> a[s] ; get the sign from stack X\r\n; if EEX was pressed show exponent digits\r\n01160 if s7 = 0\r\n01161 goto 01163\r\n01162 0 -> b[x] ; B= 00020099999000\r\n; endif\r\n01163 1 -> s9 ; S= .12....7.9.. (display_input)\r\n01164 0 -> f3 ; S= .12....7.9.b f= .12..5.. (not display_x)\r\n01165 1 -> f1 ; set auto_enter\r\n01166 rom 1\r\n00567 a <-> c[w] ; A= 01234500000002 C= 01234500000000\r\n00570 c -> a[w] ; A= 01234500000000\r\n00571 if a[m] >= 1\r\n00572 goto 00546\r\n00546 c + 1 -> c[xs] ; C= 01234500000100 (if c[xs]=9 dont goto...)\r\n00547 goto 00470\r\n00470 0 -> c[xs] ; C= 01234500000000\r\n00471 13 -> p ; P= 13\r\n00472 c - 1 -> c[x] ; C= 01234500000999\r\n00473 if b[p] = 0\r\n00474 goto 00463\r\n00463 p - 1 -> p ; P= 12\r\n00464 c + 1 -> c[x] ; C= 01234500000000\r\n00465 jsb 00473\r\n; P=11 C= 01234500000001\r\n; P=10 C= 01234500000002 (=1.2345e2 \"123.45\")\r\n00465 jsb 00473\r\n00473 if b[p] = 0\r\n00474 goto 00463\r\n00475 12 -> p ; P= 12\r\n00476 if a[p] >= 1\r\n00477 goto 00574\r\n00574 a <-> c[m]\r\n00575 rom 2\r\n01176 if c[xs] = 0\r\n01177 goto 01334\r\n01334 if c[m] >= 1\r\n01335 goto 01337\r\n01337 if p # 14\r\n01340 goto 01217\r\n01217 rom 1\r\n00620 if s8 = 0\r\n00621 goto 00531 <\/pre>\nWe see the ” 00″ bit on the end (right) of the number keyed in so far. Then when we add more digits, these go into the exponent: <\/p>\n
\r\n; press [7]\r\n;\r\n; which leads to:\r\n; A= 12345000000007\r\n02506 if c[m] = 0 ; if no prefix(es)\r\n; put C and M back\r\n02507 goto 02736\r\n02736 c <-> m ; C= 01234500000002 M= 00000000000221\r\n02737 if s3 = 0 ; if in RUN mode\r\n02740 goto 02511\r\n02511 rom 2\r\n01112 if s1 = 0 ; if not input_started\r\n01113 goto 01245 ; but it has\r\n01114 if s7 = 0 ; if not eex_pressed\r\n01115 goto 01130 ; but it was\r\n01116 a <-> c[x] ; A= 12345000000002 C= 01234500000007\r\n01117 shiftr a[w] ; A= 01234500000000\r\n01120 1 -> p ; P= 1\r\n01121 c -> a[wp] ; A= 01234500000007\r\n01122 goto 01157\r\n01157 ...\r\n; S= .12....7.9.b f= .12..5..\r\n; C= 01234500000009 P= 12\r\n00621 goto 00531\r\n\r\n; press [8]\r\n;\r\n; which leads to:\r\n; A= 12345000000078\r\n02506 if c[m] = 0 ; if no prefix(es)\r\n02507 goto 02736\r\n; put C and M back\r\n02736 c <-> m ; C= 01234500000009 M= 00000000000221\r\n02737 if s3 = 0 ; if in RUN mode\r\n02740 goto 02511\r\n02511 ...\r\n; S= .12....7.9.b f= .12..5..\r\n; A= 01234500000078 C= 01234500000080 P=12\r\n00621 goto 00531 <\/pre>\nThe “7” went into the rightmost exponent digit. Then, the “8” pushed the “7” to the left and took the rightmost position.<\/p>\n
Note that the exponent in the C register is “80”. This is because we keyed in “123.45e78” and that should be “1.2345e80” in normal scientific notation. It has added the e2 from keying in “123” to the e78 we entered into the exponent and come up with e80.<\/p>\n
The display value (A register content) still shows exactly what you keyed in “123.45e78”. <\/p>\n
If you press CHS at this point it affects the exponent sign like this: <\/p>\n
\r\n; press [CHS]\r\n; key scan addr instr\r\n; CHS (073) 01073 goto 01375\r\n;\r\n; which leads to:\r\n01375 if c[m] = 0 ; if no prefix(es)\r\n01376 goto 01140\r\n01140 c <-> m ; C= 01234500000080 M= 00000000000221\r\n01141 shiftr a[w] ; A= 01234500000078\r\n01142 if s7 = 0 ; if not eex_pressed\r\n01143 goto 01227 ; but it was\r\n01144 a <-> c[x] ; A= 01234500000080 C= 01234500000078\r\n01145 0 - c - 1 -> c[xs] ; C= 01234500000978\r\n01146 a <-> c[x] ; A= 01234500000978 C= 01234500000080\r\n01147 goto 01157\r\n01157 ...\r\n; S= .12....7.9.b f= .12..5..\r\n; A= 01234500000978 P=12 C= 01234500000924\r\n00621 goto 00531 <\/pre>\nThe A register has a “9” in the exponent sign position. This will show as a “-” in front of the other exponent digits “78”.<\/p>\n
The C register exponent is e924. This is 1000 + -76. The exponent in the C register is -76. Your HP-65 calculator has converted “123.45e-78” to “1.2345*10^2 e-78” or “1.2345e(2-78)” = “1.2345e-76”. e-76 is 100 times more than e-78, just like e80 is 100 times more than e78, because we keyed in 100 (and a bit) e-78.<\/p>\n