{"id":3762,"date":"2025-04-21T09:08:25","date_gmt":"2025-04-21T09:08:25","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=3762"},"modified":"2025-06-10T05:42:43","modified_gmt":"2025-06-10T05:42:43","slug":"4d_nackeventhandler-hash-function","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/deprecated\/4d_visi-hash-command-multitrack-only\/4d_nackeventhandler-hash-function\/","title":{"rendered":"# 4D_NackEvent(Handler) hash function"},"content":{"rendered":"\n
This is stuff you can safely ignore if it is hard to understand. It is really only needed if you need to trouble-shoot erratic communications with the 4D display<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

If something goes wrong in the communications between the SPLat and the 4D display (caused, for example, by a loose connection or some electrical noise), the 4D may send a NACK (Negative ACKnowledge) message to the SPLat. Two things happen if this occurs:<\/p>\n\n\n\n

    \n
  1. The SPLat (courtesy of the under-the-hood code generated by the hash functions) will attempt to repair the communication link by generating a special sequence of messages to the 4D display.<\/li>\n\n\n\n
  2. If you have a\u00a04D_NackEvent(Handler)<\/code>\u00a0hash function in your program, a\u00a0GoSub Handler<\/code>\u00a0will be executed. You can then have a subroutine with the label\u00a0Handler<\/code>\u00a0(or whatever you want to call it) that does something useful, like for example count the number of NACKs for debugging purposes.<\/li>\n<\/ol>\n\n\n\n

    Example:<\/p>\n\n\n\n

    Say that somewhere in your program you have the following line:<\/p>\n\n\n\n

    # 4D_ViSi  4D_NackEvent(evGotNack)\t;Declare the event handler for 4D NACK events\n<\/pre>\n\n\n\n
    You could then have an event handler subroutine that looks like this:<\/p>\n\n\n\n
    ;Event<\/a> handler for 4D NACK events
    evGotNack:     IncM        bNACKcount    ;Count NACKs
                   Return
    bNACKcount:    defBYTE<\/pre>\n\n\n\n
    The protocol handler in SPLat does not have a retry-on-NACK mechanism. Our experience is that if a NACK occurs there has most likely been a loss of message sync, and the most important thing is to re-synchronise the communications.<\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"
    This is stuff you can safely ignore if it is hard to understand. It is really only needed if you need to trouble-shoot erratic communications…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3756,"menu_order":4,"template":"","class_list":["post-3762","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"\n# 4D_NackEvent(Handler) hash function - 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=\"# 4D_NackEvent(Handler) hash function - SPLat Controls\" \/>\n<meta property=\"og:description\" content=\"This is stuff you can safely ignore if it is hard to understand. 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