[DCC] 8-pin vs 9-pin

The next release of Walthers PROTO 2000 RS-2 locos will come with a 9-pin DCC socket... I thought the NMRA DCC standard was 8 pins?

Why do some locos have 9-pin sockets instead?

What's the preferred / most common method of connecting an 8-pin decoder to a 9-pin loco?

____ Mark

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Mark Mathu
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... sorry, make that PROTO 1000

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Mark Mathu

with a 9-pin

8-pin decoder to

All of the major manufacturers make 9-pin-to-8-pin connecting cables. And TCS makes a 7-pin-to-8-pin cable for their "mini" decoders for small locos that don't have a reverse direction light.

The extra wires on the 9-pin decoders are for Function outputs. On DigiTrax decoders the green wire is F1, the violet is F2.


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Most all Digitrax HO-scale decoders have the 9-pin connection, and have for as long as I can recall (going back to the DH120's at the very least...and that's around 1998, IIRC). Lenz and NCE I believe also use them on some decoders. On the Digitrax DH12x series, those two extra wires serve no purpose and I snip 'em. On the DH14x and DH16x types, it's the function leads for F1 and F2. The nice thing about 'em is that they are keyed, so it's not possible to plug them in backwards (unlike the NMRA 8-pin). Also, they appear to be a lot more robust in use. For example, I've never broken a wire off a 9-pin decoder harness, but I have broken several 8-pin connectors (either the wire or the pin has broken or fallen off). Personally, I prefer the 9-pin over the 8-pin for the above reasons. As for the manufacturers, I think it's also because the 9-pin connector doesn't need the room and circuit board space that the 8-pin requires.

Paul A. Cutler III

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Pac Man

Mark, What Paul said.

The 9-pin plugs are called JST headers, and the "Big Four" decoder manufacturers (Digitrax, Lenz, NCE, and TCS) all make a number of decoders with JST headers.

In way of comparison, the RTR Athearns that are "DCC Quick-Plug Equipped" also use JST headers.

HTH, Stevert

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