Digitrax has released the following dealer tip:
Isambard
Grizzly Northern history, Tales from the Grizzly and news on line at isambard5935.blogspot.com
The original purpose of disptaching was as a way to get locos selected by the old buddy throttles and original UT series (before the UT4 the UT throttle could not select an address on its own). There's only 1 dispatch slot, holding the most recently dispatched loco - if you select then dispatch locos 5, 6, and 7 in that order, and then try to aquire the dispatched loco, the only one you can recover via a UT1 throttle would be #7. The others will occupy a slot each until the inactivity purge, and can be selected by any throttle that can select an address - DT400 or UT4.
The thign is, the only locos that will get purged are those set at speed step 00 AND not currently selected on any throttle. If the loco doesn;t move on speed step 1, it's entirely possible to dispatch or release a loco with the speed set to 1, but it's not moving. That loco will occupy a slot indefinitely, until you use the OpSw to purge, or clear it out with the slot monitor tool in JMRI. If you have a Locobuffer or other interface, the tools like Loconet Monitor and Slot Monitor in JMRI can give you great insight into how all this works. The Slot Monitor will show you each slot int he command station, which loco is held, and which throttle has control, as well as which functions are active. Select a loco and run it, and watch the slot - then dispatch it, and also do the Loco/Exit process and watch what happens to the slot. If you haven't already done so, set the OpSw to use the shortest purge time - there's little danger of an in-use loco being purged. There's also a lot of good info on the subject in the Loconet Personal Edition documentation available on the Digitrax site.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Dispatching a locomotive address does not release it from the 'stack'. You can use Decoder Pro to verify this. What is does do is mark it as 'available' to be taken if someone adds a new engine. You will see the old slot that was just floating around taken over by the new 'active' address. I like to think of it as a 'perspective empty' slot. I suspect that Digitrax is just not wasting machine cycles to update the slot list(and Decoder Pro is looking at that list). It would be nice if there was a 'tag' so Decoder Pro could 'highlight' a slot that was available.
Now, if you did not 'zero' the throttle, or turn off functions(like your lights), that slot will not be available to be taken over. If you click on Loconet, then the Slot Monitor; you can watch this happening. It is removed when a new engine assignment takes over the slot. Fumble fingered operators many times press other 'F' keys and leave non-existent functions turned on.
I am going to try your 'release' tip on a Zephyr with a DT400 attached tonight to see if that will 'force' off and address from a 'slot'. That would help with the operators who do not check what they have turned on before leaving the club for the night.
Jim Bernier
Modeling BNSF and Milwaukee Road in SW Wisconsin
Exactly how do you do this on a DT400 throttle? Just key in the engine address and press exit?
What I have found using Decoder Pro is as follows:
When a engine is 'Dispatched', the 'stack' table is not updated. What happens is that the 'slot' is sort of marked as a 'perspective' empty slot(at least my opinion). That slot will NOT become a 'perspective empty' if the throttle is not set to 'zero' or functions are left on. If the conditions are met, and it is a 'perspective empty' - then it may be reused. The next engine to be requested will cause the stack to be reviewed and the first available slot will be reused. You can use the 'Slot Monitor' function in Decoder Pro to watch this happen. It appears that Digitrax does not update the stack table(which is what Decoder Pro looks at). But if there is a 'request', it runs the stack table and grabs the first 'perspective empty' slot - You can see the engine number 'change' in the slot . I suspect that the reason for not constantly updating the stack table is a matter of wasting CPU cycles - there is no need to run the table until a request is presented.
Using the Slot Monitor function in Decoder Pro will also show what 'F' keys may have been activated. Some of our 'fumble finger' operators will press a key and not realize it. If we can just dial the engine number and exit, that will be faster than 'checking out' via a review with Decoder Pro. Like many others, we have had the 120 engine limit exceeded and the 'slot max' message has been presented. And we have had to clear the address/consists in the command station to resolve the problem.