{"id":3007,"date":"2025-04-17T06:31:57","date_gmt":"2025-04-17T06:31:57","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=3007"},"modified":"2025-05-07T06:43:18","modified_gmt":"2025-05-07T06:43:18","slug":"semaphore-instructions","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/","title":{"rendered":"Semaphore instructions"},"content":{"rendered":"\n

Note: The following is a short-form introduction to semaphores. The\u00a0semaphore tutorial<\/a>\u00a0has much more information, especially if you are unfamiliar with “bits” and “bytes”. Semaphores were introduced with dialect 12.<\/p>\n\n\n\n

“Semaphore” is the term we use to describe a 1-bit variable. The semaphore instructions allow you to set, clear and test semaphores in a variety of ways. You can use all of user\u00a0RAM<\/a>\u00a0as semaphores, so in a SPLat board with 128 bytes of RAM you have potentially 1024 semaphores.<\/p>\n\n\n\n

Note: Semaphores are stored in, and are part of, SPLat’s user RAM (formerly called\u00a0Data Memory<\/a>). You must take care not to accidentally use the same memory location for semaphores as well as for other types of data.<\/p>\n\n\n\n

The word semaphore is a time-honoured name in programming. Other terms that have been used are “flag” or “switch”. If your background is with relay logic you will be accustomed to “internal relay”.<\/p>\n\n\n\n

In SPLat instructions semaphores are addressed (selected) by a semaphore number ‘ss’ and a base address ‘bb’. Both these are 8-bit numbers, so they can have values between 0 and 255.<\/p>\n\n\n\n

The base address defines the byte address or location within RAM where the semaphore counting is to start. This can be any address within the existing RAM. The semaphore number is counted starting from the base address, with 8 semaphores per byte. Thus if the base address is 5, semaphore 0 will be bit 0 of location 5.<\/p>\n\n\n\n

The base address is an optional part of every semaphore instruction (not a separate register). If you omit the base address it defaults to 0. Hence, it is perfectly possible to never specify the base address, in which case the first 32 bytes of RAM will become 256 semaphores.<\/p>\n\n\n\n

In the\u00a0indexed form<\/a>, the index register is added to the base address,\u00a0not<\/em>\u00a0to the semaphore number.<\/p>\n","protected":false},"excerpt":{"rendered":"

Note: The following is a short-form introduction to semaphores. The\u00a0semaphore tutorial\u00a0has much more information, especially if you are unfamiliar with “bits” and “bytes”. Semaphores were…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2191,"menu_order":22,"template":"","class_list":["post-3007","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"\nSemaphore instructions - 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=\"Semaphore instructions - SPLat Controls\" \/>\n<meta property=\"og:description\" content=\"Note: The following is a short-form introduction to semaphores. The\u00a0semaphore tutorial\u00a0has much more information, especially if you are unfamiliar with “bits” and “bytes”. Semaphores were...\" \/>\n<meta property=\"og:url\" content=\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/\" \/>\n<meta property=\"og:site_name\" content=\"SPLat Controls\" \/>\n<meta property=\"article:modified_time\" content=\"2025-05-07T06:43:18+00:00\" \/>\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=\"1 minute\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/\",\"url\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/\",\"name\":\"Semaphore instructions - SPLat Controls\",\"isPartOf\":{\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#website\"},\"datePublished\":\"2025-04-17T06:31:57+00:00\",\"dateModified\":\"2025-05-07T06:43:18+00:00\",\"breadcrumb\":{\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Programming reference\",\"item\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"Instructions arranged by function\",\"item\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/\"},{\"@type\":\"ListItem\",\"position\":4,\"name\":\"Semaphore instructions\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#website\",\"url\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/\",\"name\":\"SPLat Controls\",\"description\":\"OEM Embedded Machine Controllers\",\"publisher\":{\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#organization\",\"name\":\"SPLat Controls\",\"url\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#\/schema\/logo\/image\/\",\"url\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-content\/uploads\/2024\/10\/logo.svg\",\"contentUrl\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-content\/uploads\/2024\/10\/logo.svg\",\"caption\":\"SPLat Controls\"},\"image\":{\"@id\":\"https:\/\/webprojects.cloud\/wordpress\/splatco\/#\/schema\/logo\/image\/\"}}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Semaphore instructions - SPLat Controls","robots":{"index":"noindex","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"og_locale":"en_US","og_type":"article","og_title":"Semaphore instructions - SPLat Controls","og_description":"Note: The following is a short-form introduction to semaphores. The\u00a0semaphore tutorial\u00a0has much more information, especially if you are unfamiliar with “bits” and “bytes”. Semaphores were...","og_url":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/","og_site_name":"SPLat Controls","article_modified_time":"2025-05-07T06:43:18+00:00","twitter_card":"summary_large_image","twitter_misc":{"Est. reading time":"1 minute"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/","url":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/","name":"Semaphore instructions - SPLat Controls","isPartOf":{"@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#website"},"datePublished":"2025-04-17T06:31:57+00:00","dateModified":"2025-05-07T06:43:18+00:00","breadcrumb":{"@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/"]}]},{"@type":"BreadcrumbList","@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/semaphore-instructions\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/webprojects.cloud\/wordpress\/splatco\/"},{"@type":"ListItem","position":2,"name":"Programming reference","item":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/"},{"@type":"ListItem","position":3,"name":"Instructions arranged by function","item":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/"},{"@type":"ListItem","position":4,"name":"Semaphore instructions"}]},{"@type":"WebSite","@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#website","url":"https:\/\/webprojects.cloud\/wordpress\/splatco\/","name":"SPLat Controls","description":"OEM Embedded Machine Controllers","publisher":{"@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#organization","name":"SPLat Controls","url":"https:\/\/webprojects.cloud\/wordpress\/splatco\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#\/schema\/logo\/image\/","url":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-content\/uploads\/2024\/10\/logo.svg","contentUrl":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-content\/uploads\/2024\/10\/logo.svg","caption":"SPLat Controls"},"image":{"@id":"https:\/\/webprojects.cloud\/wordpress\/splatco\/#\/schema\/logo\/image\/"}}]}},"_links":{"self":[{"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/spl_knowledgebase\/3007","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/spl_knowledgebase"}],"about":[{"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/types\/spl_knowledgebase"}],"author":[{"embeddable":true,"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/users\/1"}],"up":[{"embeddable":true,"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/spl_knowledgebase\/2191"}],"wp:attachment":[{"href":"https:\/\/webprojects.cloud\/wordpress\/splatco\/wp-json\/wp\/v2\/media?parent=3007"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}