Here’s how “Error” gets displayed by the HP-29C.
Using the hp29w:
; ; doing [g] [1/x] (15 74) ; S=...3.5...9.....F ; 03003: if c[m] = 0 then goto 01034 ; Divide by zero 03034: delayed rom 2 ; 03035: if n/c goto 0374 ; 01374: if n/c goto 0231 ; error: 01231: 0 -> a[w] ; A=00000000000000 01232: 0 -> c[w] ; 01233: 0 -> s 1 ; 01234: 0 -> s 2 ; 01235: p <- 13 ; P=13 01236: load constant 14 ; C=E0000000000000 P=12 01237: load constant 10 ; C=EA000000000000 P=11 01240: load constant 10 ; C=EAA00000000000 P=10 01241: load constant 12 ; C=EAAC0000000000 P= 9 01242: load constant 10 ; C=EAACA000000000 P= 8 "Error" 01243: binary ; 01244: c - 1 -> c[wp] ; C=EAACAFFFFFFFFF 01245: a exchange c[w] ; A=EAACAFFFFFFFFF C=00000000000000 01246: b exchange c[w] ; 01247: display off ; 01250: display toggle ; "Error " ; ; for i=0x400 to -1 step -1 01251: p <- 2 ; P= 2 01252: load constant 4 ; C=00000000000400 P= 1 01253: c - 1 -> c[x] ; C=000000000003FF 01254: if n/c goto 0253 ; 01253: c - 1 -> c[x] ; C=000000000003FE 01254: if n/c goto 0253 ; ... 01253: c - 1 -> c[x] ; C=00000000000001 01254: if n/c goto 0253 ; 01253: c - 1 -> c[x] ; C=00000000000000 01254: if n/c goto 0253 ; 01253: c - 1 -> c[x] ; C=00000000000FFF 01254: if n/c goto 0253 ; ; next i ; 01255: display toggle ; (display off) ; ; for i=255 to -1 step -1 01256: c - 1 -> c[wp] ; C=00000000000FFE 01257: if n/c goto 0256 ; 01256: c - 1 -> c[wp] ; C=00000000000FFD 01257: if n/c goto 0256 ; 01256: c - 1 -> c[wp] ; C=00000000000FFC 01257: if n/c goto 0256 ; ... 01256: c - 1 -> c[wp] ; C=00000000000F01 01257: if n/c goto 0256 ; 01256: c - 1 -> c[wp] ; C=00000000000F00 01257: if n/c goto 0256 ; 01256: c - 1 -> c[wp] ; C=00000000000FFF 01257: if n/c goto 0256 ; ; next i ; 01260: display toggle ; display on again ; 01261: 0 -> s 15 ; S=...3.5...9...... 01262: if 1 = s 15 then goto 01261 ; if key down, wait for up ; 01264: 0 -> s 3 ; if RUN mode 01265: if 1 = s 3 then goto 01271 ; ; ; while RUN mode and not key press 01271: if 1 = s 15 then goto 01276 ; 01273: 0 -> s 3 ; 01274: if 1 = s 3 then goto 01271 ; ; endwhile ;
It displays Error for 4 time periods, blanks the display for 1 time period – to get your attention, and then sits there with Error displayed.
Both loops use up 2 opcodes. Per the HP Journal article on the HP-67, there are about 3000 woodstock opcodes per second. The 0x400 loop is 1024×2 opcodes, about 2/3 of a second. The blanked out period is a quarter of that, just 1/6 of a second.
You have to let go of the key that you pressed. Then you can press a key to clear the Error display, or switch to PRGM mode.
Here’s what happens next (on pressing a key, so s 15 gets set):
; S=...3.5...9.....F 01274: if 1 = s 3 then goto 01271 ; 01271: if 1 = s 15 then goto 01276 ; 01276: display toggle ; 01277: delayed rom 0 ; 01300: if n/c goto 0062 ; 00062: 0 -> s 12 ; 00063: jsb 0323 ; 00323: p <- 1 ; 00324: load constant 2 ; C=00000000000F2F P= 0 00325: c -> addr ; 00326: data register -> c 15 ; C=00000000000000 00327: b exchange c[w] ; 00330: return ; 00064: if n/c goto 0114 ; 00114: jsb 0315 ; 00315: if 1 = s 2 then goto 00321 ; 00317: if 0 = s 1 then goto 00322 ; 00322: return ; 00115: binary ; 00116: delayed rom 2 ; 00117: jsb 0167 ; 01167: ... ; 0 -> s 0,4,6-8,10,13,14 01177: return ; 00120: b -> c[w] ; 00121: if 1 = s 2 then goto 00223 ; 00123: 0 -> s 1 ; 00124: 0 -> s 11 ; 00125: 0 -> c[s] ; 00126: m1 exch c ; C=0000000000006B M1=00000000000000 00127: b -> c[w] ; C=00000000000000 00130: 0 -> s 3 ; 00131: if 0 = s 3 then goto 00232 ; 00133: if 0 = s 12 then goto 00140 ; 00140: delayed rom 4 ; 00141: jsb 0000 ; 02000: ... ; get last x 02172: return ; 00142: delayed rom 2 ; 00143: jsb 0371 ; 01371: ... ; format x in A and B 01107: return ; A=0000FFFFFFFF00 B=29000000000000 00144: cpu woodstock ; 00145: display off ; 00146: display toggle ; "0.00" 00147: 0 -> s 15 ; S=...3.5...9...... 00150: if 1 = s 15 then goto 00147 ; 00152: 0 -> s 1 ; 00153: 0 -> s 3 ; 00154: if 0 = s 3 then goto 00163 ; 00156: if 0 = s 11 then goto 00165 ; 00165: 0 -> s 5 ; 00166: if 1 = s 5 then goto 00173 ; 00173: if 0 = s 15 then goto 00152 ; 00152: ...
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