{"id":3416,"date":"2025-04-18T07:44:48","date_gmt":"2025-04-18T07:44:48","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=3416"},"modified":"2025-06-10T11:11:18","modified_gmt":"2025-06-10T11:11:18","slug":"subroutines-what-are-they","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-subroutines\/subroutines-what-are-they\/","title":{"rendered":"Subroutines: What are they?"},"content":{"rendered":"\n

A subroutine is a block of code that can be invoked (“called”) from anywhere in a program, indeed from many places in a program, and when completed can return control back to the main program. Suppose you have a program where, in several places, you need to turn on a pump if analog input A is more than 39 and the digital input PumpEnable is ON. Otherwise you want the pump off. This code will do it, at least in one place within the program:<\/p>\n\n\n\n

          GoIfInOff<\/a>   PumpEnable,PumpOff
          AnInA<\/a>
          GoIfXLE<\/a>     39,PumpOff
          ON<\/a>          Pump
          GoTo<\/a>        Continue
PumpOff:  Off<\/a>         Pump
Continue: ;end of code fragment ... carry on<\/pre>\n\n\n\n
Let’s call this bit of functionality “PumpServe”. Imagine we need to do this “thing” in 3 different places in a program. We could achieve that by copying and pasting the same code into 3 places, and incidentally changing the line labels Pumpoff and Continue each time. Alternatively we could make “PumpServe” into a subroutine. <\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
The above drawing illustrates how a subroutine is used. In the main program (left) there are several references (calls) to the subroutine, using GoSub (Go to Subroutine) instructions. Each time the subroutine is called, SPLatty<\/a> jumps across to the single copy of the PumpServe code, but remembers where he came from<\/em>. When he is has done the PumpServe operation he returns to the line following the GoSub instruction. This is done with a Return instruction. Hence, a GoSub is similar to a GoTo, but has the added feature of remembering where it came from, so SPLatty can find his way back again. There is a special memory within SPLat called a “subroutine stack”, that remembers the return address.<\/p>\n\n\n\n
A subroutine may call another subroutine, and that one may in turn call another subroutine. However, you cannot “nest” subroutines indefinitely. The limit is 4 nested subroutines in dialects prior to 12, and 6 in dialect 12 and later.<\/p>\n\n\n\n
Let’s now re-write the PumpServe function as a subroutine:<\/p>\n\n\n\n
PumpServe:
          GoIfInOff<\/a>   PumpEnable,PumpOff
          AnInA<\/a>
          GoIfXLE<\/a>     39,PumpOff
          ON          Pump
          Return<\/a>
PumpOff:  Off         Pump
          Return<\/pre>\n\n\n\n
You will notice there is no longer any need to have the GoTo Continue<\/code>, as it is perfectly OK to have a Return instruction in the middle of the subroutine.<\/p>\n\n\n\n
Postscript:<\/h6>\n\n\n\n
Some programmers maintain that it is bad practice to write a subroutine with multiple return instructions, as I did above. If you are just starting out it may be a moot point. As you gain experience you may agree, on the basis that with only a single exit point from a subroutine there are fewer hazards if you alter the code for some reason. Re-writing the above example in line with this principle, we would get:<\/p>\n\n\n\n
PumpServe:\n          GoIfInOff   PumpEnable,PumpOff\n          AnInA\n          GoIfXLE     39,PumpOff\n          ON          Pump\n          GoTo        PumpRet\nPumpOff:  Off         Pump\nPumpRet:  Return<\/pre>\n","protected":false},"excerpt":{"rendered":"
A subroutine is a block of code that can be invoked (“called”) from anywhere in a program, indeed from many places in a program, and…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3414,"menu_order":0,"template":"","class_list":["post-3416","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"\nSubroutines: What are they? - SPLat Controls<\/title>\n<meta name=\"robots\" content=\"noindex, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Subroutines: What are they? - SPLat Controls\" \/>\n<meta property=\"og:description\" content=\"A subroutine is a block of code that can be invoked (“called”) from anywhere in a program, indeed from many places in a program, and...\" \/>\n<meta property=\"og:url\" content=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-subroutines\/subroutines-what-are-they\/\" \/>\n<meta property=\"og:site_name\" content=\"SPLat Controls\" \/>\n<meta property=\"article:modified_time\" content=\"2025-06-10T11:11:18+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-content\/uploads\/2025\/04\/Subroutines.gif\" \/>\n\t<meta property=\"og:image:width\" content=\"312\" \/>\n\t<meta property=\"og:image:height\" content=\"265\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/gif\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-subroutines\/subroutines-what-are-they\/\",\"url\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/tutorial-subroutines\/subroutines-what-are-they\/\",\"name\":\"Subroutines: What are they? 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