Using the protected command interface

To issue a meter command using the protected command interface, you must have a command semaphore.

To get a semaphore, read the semaphore Modbus register (see the Command interface section of the online Register list). The smart demand controller will return a 0 or a nonzero number.

• If 0 is returned, someone else owns the semaphore. You must wait for the semaphore to be available before sending a command.

• If a nonzero number is returned, you now own the semaphore. The semaphore is provided once until it is released or has been inactive for approximately 4 minutes. Once you have the semaphore, subsequent reads of the semaphore register will return 0 until you release the semaphore or it times out.

To send a meter command using the protected command interface:

1. Read the semaphore register and record the meter response. This is your semaphore.

2. Build the packet to be written to the command block.

3. Write the packet as a Modbus block write (enter the command number, semaphore, and parameters at the same time).

   Protected Command Block Example

   Command Block	Register #
   Command	2039
   Semaphore	5
   Parameters	1

4. Monitor the meter response registers for validity and completion.

   Protected Meter Response Example

   Meter Response	Register #
   Status	2039
   Result	0
   Data	1

5. Write the semaphore back to the semaphore register to release it for another master to use.