Map number simply tells you where you're at on the list of register maps. Click "next" and "prev" to scroll through the list. To advance directly to a specific map, enter the desired number in the "Map #" box, then click Update.

The local register data may be written periodically, or when it changes, or both. To send upon change (send on delta), check the first box and enter the amount by which the local register must change (more than) before being written to the remote device. To guarantee that the remote register will be written at least occasionally even if the data does not change, check the second box and enter some amount of time. This time period will be referred to as the "maximum quiet time".

Data from the local register may be manipulated before being written to the remote register. The local data is first multiplied by the scale factor. The offset is then added to it. If a bit mask is entered, and the remote register type is signed or unsigned (16-bit data), the mask will be bit-wise logical AND-ed with the data. The mask is right justified, then AND-ed with the data. The result is then left shifted back to the original position of the mask. In other words, the least significant bits of the original data will be stuffed at the position marked by the mask.

After the scaling and masking, the bit fill will be logically OR-ed into the result, but only if the mask was nonzero and was used. Both mask and fill are entered in hexadecimal.

Multiple local registers may be packed into a single remote register. To accomplish this, define two or more maps in sequence with the same remote destination. If the destination is the same, data types are 16-bit (integer or unsigned), bit masks are nonzero, and the maps are sequential, the results of all qualifying maps will be OR-ed together before being sent to the remote destination.

For the remote register to be written, enter the register type, format, number, and slave address or unit number. Size is only applicable when format is Character String, and specifies the number of characters that are to be packed 2 per register. Any size greater than 2 characters implies a multiple register write to the Modbus slave. For coils or discrete inputs, use INT-16 or UINT-16 for register format - in this case, format only affects formatting of local register data.

The repeat time may determine how often the remote register will be written. If send on delta and maximum quiet time are not checked above, clicking the "at least" button will establish a periodic update time. If send on delta is used and you wish to limit the network traffic in the event changes are frequent, click the "no more than" button and enter the minumum time that should elapse before another write to the remote device.

You have the option of enabling this map only when a selected register contains a given value. Any local register may be used as the index register. As the name implies, you can write different values to the remote register based on different maps as indexed by the index register.

Delete will remove the map number shown in the "Map #" box. Insert will insert a new map before the map number shown, and is used for placing maps between existing maps. It is not necessary to use Insert to add maps to the bottom of the list or to define any map presently having zero for a source register or "none" for remote type.

Selecting "none" for remote type effectively deletes the map even though it will still appear in the list until deleted. Unused maps at the end of the list will always show none as the type. If you wish to prevent these from being displayed, reduce the number of maps enabled.

The number of maps enabled simply limits the scope of map review so that you do not have to review a lot of unused maps. If the displayed maps are used up and you need more, increase the enabled number.