{"id":1479,"date":"2015-12-30T00:13:05","date_gmt":"2015-12-30T00:13:05","guid":{"rendered":"http:\/\/www.sydneysmith.com\/wordpress\/?p=1479"},"modified":"2017-05-14T00:40:18","modified_gmt":"2017-05-14T00:40:18","slug":"hp-65-gto","status":"publish","type":"post","link":"https:\/\/www.sydneysmith.com\/wordpress\/1479\/hp-65-gto\/","title":{"rendered":"HP-65 GTO"},"content":{"rendered":"

The GTO function is pretty straight forward in the HP-65 calculator. Here’s how it works: <\/p>\n

GTO from the keyboard looks like this:<\/p>\n

\r\n00715 rom 2\r\n01316 key -> rom         ; f= ..23.5..\r\n\r\n; [GTO]\r\n01054 goto 01347\r\n01347 rom 4\r\n02350 buffer -> rom address\r\n02351 goto 02000\r\n02054 goto 02166 <\/pre>\n
It goes on to set M[11] to 1:<\/p>\n
\r\n02120 c + 1 -> c[p]  ; C= 00100000000221 (set GTO prefix)\r\n02276 c <-> m        ; C= 00000000000000 M= 00100000000221<\/pre>\n
Then when [C] is pressed: <\/p>\n
\r\n00715 rom 2\r\n01316 key -> rom     ; f= ..23.5..\r\n\r\n; [C] pressed\r\n01033 goto 01351\r\n01351 rom 4\r\n02352 0 -> f5        ; S= ...........b f= ..23.... <\/pre>\n
It determines that GTO was pressed beforehand:<\/p>\n
\r\n02366 11 -> p        ; P= 11\r\n02367 if c[p] >= 1\r\n02370 goto 02257 <\/pre>\n
and ends up here:<\/p>\n
\r\n; doing GTO C\r\n02257 search for label   ; f= ..23....\r\n02260 (wait for ready)\r\n02261 goto 02360\r\n02360 0 -> c[m]      ; C= 00000000000221\r\n02361 c <-> m        ; C= 00000000000000 M= 00000000000221\r\n02362 ...\r\ndisplay: <\/pre>\n
There is nothing fancy in the process. It doesn’t start running. It doesn’t save a return address or activate a secondary pointer. It’s just:<\/p>\n
if GTO pressed set prefix-GTO
\nif C pressed
\n  if prefix-GTO
\n    search for label
\n    clear prefixes
\n…<\/p>\n
In a program it works the same way:<\/p>\n
\r\n00763 rom 2          ; f= ..23.5..\r\n01364 buffer -> rom address\r\n01365 goto 01000\r\n\r\n; 054 = GTO\r\n01054 goto 01347 <\/pre>\n
and <\/p>\n
\r\n00763 rom 2          ; f= ..23.5..\r\n01364 buffer -> rom address\r\n01365 goto 01000\r\n\r\n; 036 = [A]\r\n01036 goto 01351\r\n01351 rom 4\r\n02352 0 -> f5        ; f= ..23.... <\/pre>\n
The program uses GTO A but the process is the same. The only differences are: <\/p>\n
    \n
  1. It checks and re-sets the running flag again when it does a “clear status”.<\/li>\n
  2. If running it goes to get next program step instead of wait for key press.<\/li>\n<\/ol>\n
    More detail is available in 65-gto-c.txt<\/a>.<\/p>\n
    The mechanism splits the GTO and the target label into two program steps ([GTO] then [C]). This opens the door to interesting combinations like “GTO” “STO 6”. Whilst interesting, they are unlikely to do anything as most invalid combinations just clear prior prefixes. In this case the GTO would start (set a prefix) then get ignored (prefix reset) as the “STO 6” gets run.<\/p>\n
    The HP-67 merges the GTO program step so you don’t get the chance to tinker this way. Of course it has 8-bit program steps instead of the 6-bit ones that the HP-65 uses. That gives the HP-67 more scope for merging steps.  <\/p>\n","protected":false},"excerpt":{"rendered":"
    The GTO function is pretty straight forward in the HP-65 calculator. Here’s how it works:<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[16,5,39],"tags":[37,32],"_links":{"self":[{"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/posts\/1479"}],"collection":[{"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/comments?post=1479"}],"version-history":[{"count":6,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/posts\/1479\/revisions"}],"predecessor-version":[{"id":1485,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/posts\/1479\/revisions\/1485"}],"wp:attachment":[{"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/media?parent=1479"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/categories?post=1479"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sydneysmith.com\/wordpress\/wp-json\/wp\/v2\/tags?post=1479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}