Accessory Decoder Addressing

==Overview==
Accessory addresses are used to identify decoders or sub-functions thereof. Accessory Decoders are addressed by three digit numbers. The digits in question are Hexadecimal (Base 16) numbers, not Decimal (Base 10). 
 Accessory addresses are not simply different addresses that happen to identify accessory decoders instead of locomotives. Locomotives and accessories occupy different address spaces. A real-world analogy would be they live on different streets: 100 Locomotive Dr. is a different address than 100 Accessory Blvd. 
===Address Range===
Addresses are available from 1 to 2044. Each address location can control a pair of functions, usually either two solenoids for turnouts or two LEDs for signals.
Different manufacturers view this range in one of two ways:
#) 511 decoder addresses, each with 4 sub-addresses, or
#) 2044 individual output addresses
Not all command stations support all of the possible addresses in that range.
 Accessory decoders are addressed differently than multifunction decoders. Each address defines an individual cell, by changing that cell turnout motors or signal aspects can be activated. 
==== Basic Addressing Structure ====
In this mode the decoder is configured with a 9-bit address which is considered to be the base address. The decoder can then have up to four pairs of outputs at this address.
Basic Accessory Decoder Addressing	Basic Accessory Decoder Addressing	Basic Accessory Decoder Addressing	Basic Accessory Decoder Addressing	Basic Accessory Decoder Addressing	Basic Accessory Decoder Addressing
Byte 1 	Byte 1 	Byte 2 	Byte 2 	Byte 2 	Byte 2
Flags 	Address Bits 	Flags 	Address Bits 	Command Bit 	Data Bits
10 	AAAAAA 	1 	AAA 	C 	D1D0Dx
The first pair of flags indicate the address is for an accessory decoder. The second flag indicates a two- or three-byte command. The flags also seperate the first and second bytes.
The Command and Data bits are used to determine the state of and which output is to be used.
A total of 2044 address are available using both the 511 possible address and the four available outputs (D1D0). When used with turnout motors, the Data bits are used in the following manner: The first two (D1D0) indicate the output (one of four), Dx defines which output will be used if configured for a three-wire device. 
==== Extended Addressing Structure ====
Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing	Extended Accessory Decoder Addressing
Flags 	Address Bits 	Flags 	Address Bits 	Flags 	Address Bits 	Aspect 1 	Aspect 2
Byte 1 	Byte 1 	Byte 2 	Byte 2 	Byte 2 	Byte 2 	Byte 3 	Byte 3
10 	AAAAAA 	0 	AAA 	0 	AA1 	YYYY 	ZZZZ
 Extended Accessory Decoder Addresses are occasionally referred to as an 11-bit address on account of having two additional address bits. 
 The second flag is set to zero, indicating a three-byte packet is in use. The third byte is indicated by the yellow background.
===Special Addresses===
The NMRA reserves addresses 2045 to 2048 for broadcasting to all accessory decoders.
===Configuration===
Many accessory decoders use learning to configure their address. In learning mode a throttle sends an accessory command to the desired address. 
When configuring the decoder using the CV method, the NMRA defines two ways to set the address CVs:
====Decoder Address====
In this mode the decoder is configured with a 9-bit address, which is considered to be the base address. The decoder can then have up to four pairs of outputs at this address.
====Output Address====
In this mode the decoder is configured with an 11-bit address which is considered to be the specific output pair address. The decoder may have only one output pair. 
===Comparison of Various Accessory Decoders===
Manufacturer	Model 	Output Address Range	Output Pairs	Learning	CV Method
DCC Concepts	AD1 	1-2044 	1 	Yes 	No
Digitrax 	DS64 	1-2044 	4 	Yes 	No
Digitrax 	SE74 	 	4 	 	Yes
Digitrax 	DS78V 	 	8 	 	Yes
Digitrax 	DS74 	 	4 	 	Yes
Digitrax 	DS44 	 	4 	 	
Digitrax 	DS52 	 	2 	 	
Gaugemaster 	DCC30 	1-127 	4 	No 	Yes
Lenz 	LS100/110	1-256 	4 	Yes 	Yes
Zimo 	MX820E 	1-2044 	1 	No 	Yes
===See Also===
Address Range: How addresses are partitioned 
===External links===
Hexadecimal
Category:Decoder
Category:Accessory Decoder