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write_protection

Modbus Write Protection

The SS20's Write Protection functions are used to block modbus write commands from passing through the SS20. Write protection can be enabled for each input port individually. This function is useful if two different parties need to read information from a device(s) but only one should have access to write to the device.

Sometimes you may want to limit the write access to only certain registers (eg. for writing an index value for polling historical records) Up to 6 register ranges can be allowed through as an exception to the 'block write commands' function.

Block Modbus Write commands When Checked the SS20 will block write all Modbus write commands from passing through the specified input port unless they are for registers listed in the following exceptions table. Function codes blocked by the write protection include 05, 06, 15, 16, 21, 22, and 23.
Enable Check box to enable an exception range of addresses to allow write commands to. This allows the SS20 to block all write commands through the port except for up to 6 specific register rangers. These ranges may be used to allow writes to index registers for historical data polling but block writes to operational control registers.
Start Reg first register address of the exception range. Register address is how it appears in the message, no offset is implied. If the devices register map infers an offset of 1, you may need to subtract one from the register number listed on the map.
End Reg Last register address of the exception range. Register address is how it appears in the message, no offset is implied. All registers addressed in multi-register write function codes must fall within the exception range or the message will be blocked.
write_protection.txt · Last modified: 2016/10/23 10:05 by dmeier