ModBus: Communication Control Blocks

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 Control Block (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 instruction.

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.

Examples

The following table is a copy of the one above (with the master column removed) used as a worksheet for a slave.

In your SPLat program this configuration would look like this:

                NVEM0           ;Start of NVEM data
ModBusCCB:
                NV0Byte         1       ;Protocol
                NV0Byte         3       ;Address
                NV0Byte         0       ;Character = 8,1,N
                NV0Byte         5       ;9600
                NV0Byte         255     ;Not used - set to 255
                NV0Byte         255     ;Not used - set to 255
                NV0Byte         255     ;Not used - set to 255
                NV0Byte         255     ;Not used - set to 255
                NV0Byte         255     ;Not used - set to 255
                NV0Byte         10      ;Message gap 100mS
                NV0Byte         100     ;Query timeout 1S
                NV0Byte         3       ;Query attempts
                NV0Byte         255,255,255,255,255,255,255,255 ;Not used - set to 255