A DCC-EX EX-CSB1 makes RailCom cutouts, on the development firmware
Before any decoder can be heard, the command station has to make the gap for it to speak in. The station on this bench is a DCC-EX EX-CSB1, the ESP32-based one. The RailCom cutout for this board arrived on the development line and has not yet reached a production release, so getting it means building the development firmware. This post is how, and what the result looks like on a scope.
Building it
The DCC-EX installer offers the latest production version, the latest development version, or a specific version. The build on this bench is development version 5.9.10, which I got by choosing “select a specific version” and entering 9.9.9; that gave me the head of the development branch. The previous development build, 5.9.9, would not compile for me; 5.9.10 did.
One warning for anyone with the older Arduino Mega station: the development line dropped the AVR boards at 5.9.0, so a Mega stays on 5.6 and this does not apply to it.
Switching it on
On the CSB1 the cutout is a per-track setting, not the global one. The global command reports itself on and does nothing on this board; what works is to declare the track as main and then add the RailCom modifier:
<= A MAIN>
<= A RAILCOM>The setting does not survive a reboot, so it goes in the startup automation file or gets sent again after power-up.
What the scope shows
With a sense resistor in one track lead and a PicoScope across it, there is a cutout after every packet, including idle packets, with the two rails shorted together for its length as RCN-217 requires. The standard lets a station end the cutout anywhere between 454 and 488 microseconds after the packet’s end bit; this one holds it to the full 488, the longest allowed. A decoder’s reply has to be finished by 454 whatever the station does, and the longest replies seen so far on this bench do so with a few microseconds to spare. Those are numbers the detector design has to respect, and they are the kind of thing you learn from the track output, not from reading the firmware.
A later post is what happened when a decoder was given that gap to speak in.
Tags: bench, command-station, dcc-ex, railcom