So today I went on site for interfacing a NetLinx AMX system with Sauter HVAC system. The HVAC system is interfaced through a PC that translates internal bus to more regular Modbus\/Jbus protocol.
\n
\nModbus is a pretty simple protocol but its implementation is not so simple due to three facts:<\/p>\n
STACK_VAR
\nCHAR TEMP[6]
\nCHAR INTERRO_A_ENVOYER[8]
\nLONG TEMP_1
\nLONG XFLG
\nLONG I
\nLONG J
\nLONG CRC
\n{
\nTEMP = \u00ab\u00a01,3,0,((ETAPE-1)*4),0,2\u00a0\u00bb
\nCRC = $FFFF
\nFOR(I=1;I<7;I++)
\n{
\nTEMP_1 = TEMP[I]
\nFOR(J=1;J<9;J++)
\n{
\nXFLG = (CRC^TEMP_1) & $0001
\nCRC = CRC >> 1
\nIF(XFLG<>0)
\n{
\nCRC = CRC ^ $A001
\n}
\nTEMP_1 = TEMP_1 \/ 2
\n}
\n}
\nI = CRC \/ 256
\nJ = CRC – (I*256)
\nINTERRO_A_ENVOYER = \u00ab\u00a0TEMP,J,I\u00a0\u00bb
\nSEND_STRING dvCLIM,INTERRO_A_ENVOYER
\n}<\/p><\/blockquote>\nThat sample computes automatically checksum for a read message of two bytes \ud83d\ude42<\/p>\n
- Second problem is for answer you get back from HVAC as temperature value is coded with IEEE system. I looked at it on internet but it looks pretty complex to encode, so for now I just do a comparison between know values and it allows me to get correct value, at price of extra comparison work but it functions perfect \ud83d\ude42 If someone already did a piece of code in NetLinx to encode\/decode IEEE value, I’m interested in !<\/li>\n
- Last point very important with Modbus protocol is that it doesn’t speak by itself \ud83d\ude41 So each time you want to know something you have to issue a read command. So best way is to use a timeline you run in background that continuously asks values at system so you keep always value up to date \ud83d\ude42<\/li>\n<\/ol>\n
Hope it helped you, and feel free to ask questions you might have in comments !<\/p>\n","protected":false},"excerpt":{"rendered":"
So today I went on site for interfacing a NetLinx AMX system with Sauter HVAC system. The HVAC system is interfaced through a PC that translates internal bus to more regular Modbus\/Jbus protocol.<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[46],"tags":[],"class_list":["post-665","post","type-post","status-publish","format-standard","hentry","category-technology"],"_links":{"self":[{"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/posts\/665","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.domedia.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=665"}],"version-history":[{"count":1,"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/posts\/665\/revisions"}],"predecessor-version":[{"id":666,"href":"https:\/\/www.domedia.net\/index.php?rest_route=\/wp\/v2\/posts\/665\/revisions\/666"}],"wp:attachment":[{"href":"https:\/\/www.domedia.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=665"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.domedia.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=665"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.domedia.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}