Document CV29 output/board addressing mode

[chrisridd]

Your extension to CV29 could be better documented!

As far as I can see it just changes two things:

1. The way the accessory address is computed
2. Which accessory callback is used i.e. notifyDccAccTurnoutBoard or notifyDccAccTurnoutOutput

Neither of which is very clear - which mode should an accessory implementor use and why?

[MicroBahner]

Well. I don't see any 'extension' to CV29. The meaning of the bits in CV29 is well documented in the Nmra papers. Bit 6 defines whether the decoder uses board adressing or output adressing. And the corresponding callback is used when an accessory packet is received.

Edit: If you implement an accessory decoder and use one of the addressingmodes exclusively you should inhibit changing of bit 6 in CV29.

Regards Franz-Peter

[gbglacier]

Hi,
This is just downloaded from the NMRA.org site. Bit 6 is not
  defined. Any change from the current default
  implementation of any addressing scheme should be avoided.
Configuration Variable 29 Configurations Supported
  Bit 0 = Locomotive Direction: "0" = normal, "1" = rev 215 ersed.
  This bit controls the locomotive's forward and
  backward direction in digital mode only. Directional sensitive
  functions, such as headlights (FL and
  FR), will also be reversed so that they line up with the
  locomotive’s new forward direction. See S-
  9.1.1 for more information.
  Bit 1 = FL location: "0" = bit 4 in Speed and Direction
  instructions control FL, "1" = bit 4 in function group
  220 one instruction controls FL. See S-9.2.1 for more information.
  Bit 2 = Power Source Conversion: "0" = NMRA Digital Only, "1" =
  Power Source Conversion Enabled, See
  CV#12 for more information,
  Bit 3 = Bi-Directional Communications: "0" = Bi-Directional
  Communications disabled, "1" = Bi-Directional
  Communications enabled. See S-9.3.2 for more information.
  225 Bit 4 = Speed Table: "0" = speed table set by configuration
  variables #2,#5, and #6, "1" = Speed Table set by
  configuration variables #66-#95
  Bit 5 = "0" = one byte addressing, "1" = two byte addressing (also
  known as extended addressing), See S 9.2.1
  for more information.
  Bit 6 = Reserved for future use.
  230 Bit 7 = Accessory Decoder: "0" = Multifunction Decoder, "1" =
  Accessory Decoder (see CV #541 for a
  description of assignments for bits 0-6)
  *Note If the decoder does not support a feature contained in this
  table, it shall not allow the corresponding bit to be
  set improperly (i.e. the bit should always contain its default
  value).
Have fun!  :-)
  Best regards,
  Geoff Bunza

On 12/14/2019 5:29 AM, Franz-Peter
  wrote:

  Well. I don't see any 'extension' to CV29. The meaning of the
    bits in CV29 is well documented in the Nmra papers. Bit 6
    defines whether the decoder uses board adressing or output
    adressing. And the corresponding callback is used when an
    accessory packet is received.
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    Geoff Bunza
    gbglacier@comcast.net
    scalemodelanimation.com
     

[MicroBahner]

Hi Geoff, the definitions you posted are the definitions for a multifunction (=locomotiv) decoder. This issue is about an accessory decoder. The meaning of the bits in CV29 ist different between these types of decoders. The meaning of the bits for an accessory decoder is defined later in that paper at pages 10/11:

Configuration Variable 29 [541] Accessory Decoder Configurations Supported Bits 0-2 = Reserved for future use. Bit 3 = Bi-Directional Communications: "0" = Bi-Directional Communications disabled, "1" = Bi-Directional 425 Communications enabled. See S-9.3.2 for more information.` Bit 4 = Reserved for future use.S-9.2.2 Copyright 1999-2012 by National Model Railroad Association, Inc. Page 11 of 12 Bit 5 = Decoder Type: ‘0’ = Basic Accessory Decoder; ‘1’ = Extended Accessory Decoder Bit 6 = Addressing Method: ‘0’= Decoder Address method; ‘1’ = Output Address method Bit 7 = Accessory Decoder: = "0" Multifunction Decoder (See CV-29 for description of bit Assignments for bits 430 0-6), "1" = Accessory Decoder. If bit 7 = 1, then the decoder may ignore the two most-significant bits of the CV number in Service Mode only. Using this feature CV513 becomes CV1, etc. Decoders which perform the translation must clearly

There you can see that Bit 6 defines the adressing method. Regards Franz-Peter

[gbglacier]

Hi Franz-Peter,
Got it. Thanks for contributing to my continuing
    education.
Whatever way the JMRI default of continuous
    addressing, rather than decoder and "page" or whatever it was
    called, should be left as the default for the NmraDcc library,
    in my opinion. This is as the library was, as well.
Have fun!  :-)
    Best regards,
    Geoff

On 12/21/2019 12:05 PM, Franz-Peter
  wrote:

  Hi Geoff,
    the definitions you posted are the definitions for a
    multifunction (=locomotiv) decoder. This issue is about an
    accessory decoder. The meaning of the bits in CV29 ist different
    between these types of decoders. The meaning of the bits for an
    accessory decoder is defined later in that paper at pages 10/11:

    Configuration Variable 29 [541] Accessory Decoder
      Configurations Supported
      Bits 0-2 = Reserved for future use.
      Bit 3 = Bi-Directional Communications: "0" = Bi-Directional
      Communications disabled, "1" = Bi-Directional
      425 Communications enabled. See S-9.3.2 for more information.`
      Bit 4 = Reserved for future use.S-9.2.2
      Copyright 1999-2012 by National Model Railroad Association,
      Inc. Page 11 of 12
      Bit 5 = Decoder Type: ‘0’ = Basic Accessory Decoder; ‘1’ =
      Extended Accessory Decoder
      Bit 6 = Addressing Method: ‘0’= Decoder Address method; ‘1’ =
      Output Address method
      Bit 7 = Accessory Decoder: = "0" Multifunction Decoder (See
      CV-29 for description of bit Assignments for bits
      430 0-6), "1" = Accessory Decoder. If bit 7 = 1, then the
      decoder may ignore the two most-significant
      bits of the CV number in Service Mode only. Using this feature
      CV513 becomes CV1, etc.
      Decoders which perform the translation must clearly

  There you can see that Bit 6 defines the adressing method.
    Regards
    Franz-Peter
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-- 

    Geoff Bunza
    gbglacier@comcast.net
    scalemodelanimation.com
     

[MicroBahner]

Hi Geoff, yes, I think we're not going to change this behavior of the library. When initializing the library you can set the default adressing mode as you want. If you don't want it to be changed later, you have to inhibit changing the bit in CV29. That must be done in the sketch.

As I understood, the question in this issue was about a better documentation. But the library complies with the standard - also in this respect. I have therefore pointed out that it is not an extension. In my opinion we cannot describe the standards in the library documentation.

Best regards Franz-Peter

[chrisridd]

Like Geoff, I'd only found the definition for CV 29 for locomotive decoders - but now I can see the different CV 29 definitions for accessory decoders I concur that this library's use of bit 6 is quite standard and correct and does not need changing.

However I still do not understand what the mode actually means, which was my main question. Do you have a reference to the NMRA docs that explains it?

[MicroBahner]

Hi, The difference between output addressing and decoder addressing is described in the same NMRA document (9.2.2). This can be found in the description of the CV's 513 and 521 which define the decoder address (on pages 9/10). But in my opinion the description is a little bit hard to understand.. A graphic, which should make things clearer, can be found here (its on a german website).

Decoder addressing is rather historical. It is based on the first decoders, which could always control 4 turnouts. The decoder was addressed via the 'main address', and the turnouts via a sub-address(0..3). Such decoders still exist. Output adressing combines both addresses into one accessory-address, and the turnouts/signals are numbered continuously. The decoder itself has no address. This is more flexible. A decoder can control an arbitrary number of accessories. The address in CV513/521(1/9) is usually the address of the first controlled accessory in the line.

[kiwi64ajs]

I don't think there is an issue here apart from the DCC Standards being not precise enough, but I believe the code is doing the right things in terms of handling the Output Addressing Mode