5.5. 32/64-bit Value Settings

The official Modbus protocol (in both the original Modbus specification and the current Modbus specification) only allows 1-bit and 16-bit integer values to be transferred. Many manufacturers have extended the protocol to allow 32-bit and 64-bit values, and also to allow floating-point values. Fortunately, everyone seems to have used the IEEE format for floating-point numbers, but that is where the agreement ends. The 32/64-bit Values group of settings (see Section 5.1, “Adding Device Types”) enables you to configure ModSnmp to handle all implementations of 32/64-bit values that we know of.

These three options (Little-endian, Word-registers, and Word-count) allow 8 possible variations of 32/64-bit value handling. At least 5 of these variations have actually been used in devices, so you may need to carefully read documentation, or to experiment, to determine which variation a particular device uses. The default settings (all options selected) should work with Modicon/Schneider devices. For Enron/Daniel devices you will probably need to deselect all the options.

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