{"id":3336,"date":"2025-04-18T05:06:07","date_gmt":"2025-04-18T05:06:07","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=3336"},"modified":"2025-06-10T09:32:36","modified_gmt":"2025-06-10T09:32:36","slug":"modbus-communication-control-blocks","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/tutorials-application-notes-and-white-papers\/serial-communications\/modbus\/modbus-communication-control-blocks\/","title":{"rendered":"ModBus: Communication Control Blocks"},"content":{"rendered":"\n

Since this was written we have introduced Hash commands. The Open_Serial<\/a><\/code> hash command make this much simpler to do.<\/p>\n\n\n\n

ModBus is selected and configured via a suitable Communications Control Block<\/a> (CCB). The following table summarizes the various parameters in the CCBs for ModBus. Entries are hyper-linked to detailed descriptions. If you are using a ModBus protocol you must set up a CCB with the specified parameters and then invoke it in your program with a ComSetCCB<\/a> <\/code>instruction.<\/p>\n\n\n\n

The table contains a spare column so you can print it out and use it as a work sheet. Click on each entry to get a detailed expose.<\/p>\n\n\n\n

Byte<\/th>Slave RTU<\/th>Master RTU<\/th>Notes<\/th><\/tr>
0<\/td>1<\/td>2<\/td> <\/td><\/tr>
1<\/td>DevAddr<\/a><\/td>0<\/td> <\/td><\/tr>
2<\/td>CharProfile<\/a><\/td>CharProfile<\/a><\/td> <\/td><\/tr>
3<\/td>BaudRate<\/a><\/td>BaudRate<\/a><\/td> <\/td><\/tr>
4<\/td>Not used – set to 255<\/td> <\/td><\/tr>
5<\/td>Not used – set to 255<\/td> <\/td><\/tr>
6<\/td>Not used – set to 255<\/td> <\/td><\/tr>
7<\/td>Not used – set to 255<\/td> <\/td><\/tr>
8<\/td>Not used – set to 255<\/td> <\/td><\/tr>
9<\/td>MessageGap<\/a><\/td>MessageGap<\/a><\/td> <\/td><\/tr>
10<\/td>0<\/td>QryTimeout<\/a><\/td> <\/td><\/tr>
11<\/td>0<\/td>QryAttempts<\/a><\/td> <\/td><\/tr>
12<\/td>Not used – set to 255<\/td> <\/td><\/tr>
13<\/td>Not used – set to 255<\/td> <\/td><\/tr>
14<\/td>Not used – set to 255<\/td> <\/td><\/tr>
15<\/td>Not used – set to 255<\/td> <\/td><\/tr>
16<\/td>Not used – set to 255<\/td> <\/td><\/tr>
17<\/td>Not used – set to 255<\/td> <\/td><\/tr>
18<\/td>Not used – set to 255<\/td> <\/td><\/tr>
19<\/td>Not used – set to 255<\/td> <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Examples<\/h6>\n\n\n\n

The following table is a copy of the one above (with the master column removed) used as a worksheet for a slave.<\/p>\n\n\n\n

Byte<\/th>Slave RTU<\/th>Example value<\/th><\/tr>
0<\/td>1<\/td>1<\/td><\/tr>
1<\/td>DevAddr<\/a><\/td>3<\/td><\/tr>
2<\/td>CharProfile<\/a><\/td>0 (8,1,N)<\/td><\/tr>
3<\/td>BaudRate<\/a><\/td>5 (9600)<\/td><\/tr>
4<\/td> <\/td>Not used – set to 255<\/td><\/tr>
5<\/td> <\/td>Not used – set to 255<\/td><\/tr>
6<\/td> <\/td>Not used – set to 255<\/td><\/tr>
7<\/td> <\/td>Not used – set to 255<\/td><\/tr>
8<\/td> <\/td>Not used – set to 255<\/td><\/tr>
9<\/td>MessageGap<\/a><\/td>10 (x10mS = 100mS)<\/td><\/tr>
10<\/td>QryTimeout<\/a><\/td>0 (Not used in slave)<\/td><\/tr>
11<\/td>QryAttempts<\/a><\/td>0 (Not used in slave)<\/td><\/tr>
12<\/td> <\/td>Not used – set to 255<\/td><\/tr>
13<\/td> <\/td>Not used – set to 255<\/td><\/tr>
14<\/td> <\/td>Not used – set to 255<\/td><\/tr>
15<\/td> <\/td>Not used – set to 255<\/td><\/tr>
16<\/td> <\/td>Not used – set to 255<\/td><\/tr>
17<\/td> <\/td>Not used – set to 255<\/td><\/tr>
18<\/td> <\/td>Not used – set to 255<\/td><\/tr>
19<\/td> <\/td>Not used – set to 255<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

In your SPLat program this configuration would look like this:<\/p>\n\n\n\n

                NVEM0           ;Start of NVEM<\/a> data<\/code>
ModBusCCB:<\/code>
                NV0Byte         1       ;Protocol<\/code>
                NV0Byte         3       ;Address<\/code>
                NV0Byte         0       ;Character = 8,1,N<\/code>
                NV0Byte         5       ;9600<\/code>
                NV0Byte         255     ;<\/code>Not used - set to 255
                NV0Byte         255     ;<\/code>Not used - set to 255
                NV0Byte         255     ;<\/code>Not used - set to 255
                NV0Byte         255     ;<\/code>Not used - set to 255
                NV0Byte         255     ;<\/code>Not used - set to 255
                NV0Byte         10      ;Message gap 100mS<\/code>
                NV0Byte         100     ;Query timeout 1S<\/code>
                NV0Byte         3       ;Query attempts<\/code>
                NV0Byte         255,255,255,255,255,255,255,255 ;Not used<\/code> - set to 255<\/pre>\n","protected":false},"excerpt":{"rendered":"
Since this was written we have introduced Hash commands. The Open_Serial hash command make this much simpler to do. ModBus is selected and configured via a suitable Communications…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3328,"menu_order":0,"template":"","class_list":["post-3336","spl_knowledgebase","type-spl_knowledgebase","status-publish","hentry"],"acf":[],"yoast_head":"\nModBus: Communication Control Blocks - 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=\"ModBus: Communication Control Blocks - SPLat Controls\" \/>\n<meta property=\"og:description\" content=\"Since this was written we have introduced Hash commands. The Open_Serial hash command make this much simpler to do. 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