Introduction to DCC/Moving a Locomotive Onto a Siding

For the operational examples below, consider again the Abstract Functional Block Diagram. In the diagram, note the locomotive headlights, indicating their forward directions.
 
DCC - How It Works Operationally: An Operator Wants to Move #9905 Onto the Siding 	DCC - How It Works Operationally: An Operator Wants to Move #9905 Onto the Siding 	DCC - How It Works Operationally: An Operator Wants to Move #9905 Onto the Siding
From the Operator's Perspective 	What's Going On Under the Covers 	Result on Layout
The Operator arbitrarily selects the 2nd Throttle and enters the address of the locomotive to be controlled - 9905.	2nd Throttle saves address 9905. All subsequent commands from 2nd Throttle will be sent to Decoder 9905. 	None.
Wanting Locomotive 9905 to clear the points of the turnout, the Operator selects Reverse direction. 	2nd Throttle saves direction as Reverse. All subsequent commands from 2nd Throttle will specify Locomotive 9905 is to move in the reverse direction. 	None.
The Operator increases throttle speed. 	2nd Throttle interprets the Operator's throttle action as, "Set speed to Speed Step 2" [presumed to be previously set to "Speed Step 0"], and sends a Speed Step 2 / Reverse command, addressed to 9905. The Command Station constructs, and then broadcasts on the Booster Bus, to all Boosters, a DCC packet addressed to 9905, specifying Speed Step 2 / Reverse. All Boosters simultaneously place the packet on their respective tracks. All Decoders receive the packet. All Decoders except Decoder 9905 ignore the packet, as it is not addressed to them. Decoder 9905 executes the command and applies a low-level [speed step 2], reverse voltage [reverse direction] to the locomotive's motor.	Locomotive 9905 eases back from the turnout.
The Operator decreases throttle speed. 	2nd Throttle interprets the Operator's throttle action as, "Set speed to Speed Step 0", and sends a Speed Step 0 / Reverse command, addressed to 9905. The Command Station, Boosters and Decoders all respond as above, but now for the Speed Step 0 / Reverse Command. 	Locomotive 9905 comes to a stop, clear of the turnout's points.
The Operator selects "1001" ,the address of the turnout motor's Stationary Decoder. 	2nd Throttle saves address 1001. All subsequent commands from 2nd Throttle will be sent to Decoder 1001. 	None.
The Operator selects "Throw", to switch the turnout to the siding. 	2nd Throttle sends a Throw command to addressed to 1001. The Command Station, Boosters and Decoders all respond as above, but now for the Throw Command addressed to Decoder 1001. Decoder 1001 activates the turnout motor, in the correct direction to throw the turnout to the siding. 	The turnout motor moves the turnout points to the thrown position.
The Operator enters the address 9905. 	2nd Throttle saves address 9905. All subsequent commands from 2nd Throttle will be sent to Decoder 9905. 	None.
The Operator selects Forward direction. 	2nd Throttle saves direction as Forward. All subsequent commands from 2nd Throttle will specify Locomotive 9905 is to move in the forward direction. 	None.
The Operator increases throttle speed. 	2nd Throttle interprets the Operator's throttle action as, "Set speed to Speed Step 4 / Forward", and sends a Speed Step 4 command addressed to 9905. The Command Station, Boosters and Decoders all respond as above, but now for the Speed Step 4 / Forward command addressed to Decoder 9905. 	Locomotive 9905 moves forward thru the turnout, onto the siding.
The Operator decreases throttle speed. 	2nd Throttle interprets the Operator's throttle action as, "Set speed to Speed Step 0 / Forward", and sends a Speed Step 0 command addressed to 9905. The Command Station, Boosters and Decoders all respond as above, but now for the Speed Step 0 / Forward command addressed to Decoder 9905. 	Locomotive 9905 comes to a stop on the siding.