With DCC, you have Function Control of the loco's lights and other electrical devices on board. Each decoder responds to Function Controls sent to its two- or four-digit address, whichever the decoder is programmed to respond to. When a loco is MU-consisted to another address, then it gets it's motor control from the consist address, but it's Function Control is still from the decoders original two- or four-digit address.

There is a feature called Decoder-Assisted Consisting (DAC). This is one of four ways to MU consist two or more locos together to operate as one unit. There is another feature called DAC Function Control. It is used to transfer Function Controls from the loco address to the Decoder Assisted Consisted address. Refer to Decoder-Assisted Consisting for more information about DAC and MU consisting.

When building an MU consist, a consist address is chosen - an address used to send control packets to the entire consist. Most people use the base address of the lead loco for the consist address. But some people use a phantom consist address (an address that is not used by any loco on the layout) to consist all locos to. In this case, the phantom is the lead loco and all real locos in the consist are consisted to that phantom.

Any loco that is consisted to the consist address will NOT have Function Control of the lights or anything else on the loco from that consist address. The only thing that will respond from that consist address is the motor's speed and direction commands. You have to select that loco's base address to operate its functions independently of the consist's speed and direction. This is one situation where Digitrax's dual -knob throttles come in handy. While controlling the consist speed, direction, and lead loco's functions with the right knob, you can select consisted loco addresses into the left knob to control the lights and other functions there.

For example, let's say that you're building a consist with the lead loco's address of 25 and you are going to consist loco #10 to it. When the consist is complete, both locos in the consist will operate speed and direction from the consist address of 25. However, when you turn the lights on or off (or any other function, for that matter), only the lights on the loco with the base address of 25 will respond. To operate the lights on loco #10, you will have to select address 10 to control those functions. People using Digitrax's two-knob throttle usually leave consist control in the right knob and select the consisted loco into the left knob for Function Control. Even though you will have loco #10 selected into the left knob for Function Control, you will not be able to control it's speed or direction there. Speed and direction of all locos in the consists is controlled only from the consist address.

However, there could be a situation where you might want to have consisted locos' functional control to respond from the consist address. This is where DAC Function Control comes in.

With DAC Function Control, you can program each decoder to provide DAC Function Control for any function the decoder has. Each function is handled separately. This allows you to provide Function Control of one function and not another, if desired. For example, you probably wouldn't want the headlight of the second loco to go on and off with the lead loco's, but you may want its horn and bell to operate even though it's not the lead loco. In this case, you would program the headlight to not have control, but functions 1 and 2 (bell and horn) to have Function Control with the DAC consist address. In this situation, the headlight can still be controlled from that decoder's base address while the bell and horn are controlled from either consist or base address.

DAC Function Control does not affect the functional control when it is not consisted, but only when it is consisted via Decoder-Assisted Consisting. The decoder knows when to provide control and when not to, based upon whether or not there's an address in CV19.

When the loco is not consisted, there is no address in the DAC address CV (CV19). As such, the loco gets its motor and Function Control from the base address. If there is an address in the DAC CV, then the loco gets its motor control from the DAC address and checks the DAC Function Control CVs to see which Function Control to get commands from the DAC address. This sounds cumbersome in the description, but all these decisions are made by the decoder in millionths of a second.

Note that DAC Function Control only works when consisting via Decoder-Assisted Consisting. It does not work with Command Station Consisting.

This feature is handled completely within the decoder. So if you want DAC Function Control, you have to be sure the decoder you get has this feature.

Train Control Systems, NCE, and Throttle Up!'s SoundTraxx decoders have this feature implemented.

Digitrax decoders do not have this feature implemented.

Each function is specifiable. CV21 controls functions 1 through 8 - starting with bit zero for Function 1 through bit 7 for Function 8. CV22 uses bit zero to control Function 0 when going forward and bit 1 to control Function 0 when in reverse. As such, you need a system or other method to program CVs 21 and 22. See CV Bit Manipulation for more information about bit control.

All of Digitrax's current systems can program any value into these CVs.

DAC Function Control is not intrusive. It comes turned off and you do not need to bother with it unless you want to use it in conjunction with Decoder-Assisted Consisting.