FAQ:Will an Accessory Decoder's Extended Address interfere with Mulitfunction Decoders

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DCC Categories Beginner, Multifunction Decoder, Stationary Decoder
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As demonstrated by this table, the permissible DCC Addresses have been partitioned into distinct groups.

Addresses from:

  1. $01 to $7F are the "seven bit" Multifunction Decoder Primary Addresses.
  2. $80 – $BF as the value of the first byte of two encompass the Basic Accessory Decoder 9–bit or Extended Accessory Decoder 11–bit addresses
  3. $C0 – $E7 are the "fourteen bit" Multifunction Decoder Extended Addresses
  • Any address where the first address byte (of two bytes) is a value from $8 to $B is an accessory decoder address. An accessory decoder would not recognise any address where the first byte is not in that defined range.
  • Accessory and Extended addressing modes require two bytes to form the complete address.
  • The Primary Address uses a single byte. CV29 determines the addressing mode in use. When Extended Address Mode (EAM) is active, the decoder expects to see two Address Bytes.
    • The Primary address byte can intrude into Accessory Decoder space as direction information is contained within the address byte. As it is a single byte, the accessory decoder will ignore that value.
The "$" indicates the number is expressed in Hexadecimal, not decimal.