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R8249 Hornby: 4 Function  Locomotive DCC Decoder NMRA Compliant

R8249 Hornby: 4 Function Locomotive DCC Decoder NMRA Compliant

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Product Description

The Hornby locomotive decoders may be used with all standard digital control equipment that conforms to the NMRA standards.

  • Control of the motor’s rotational speed (load compensation)
  • Acceleration and deceleration separately adjustable
  • Selectable for operation with 14, 28, 128 speed steps
  • Programming on main track
  • Four On/Off function outputs.Two of the function outputs are dedicated for the head / tail lights.
  • Operation on standard DC systems (analogue operation) possible
  • Motor overload current protection
  • With NMRA RP-9.1.1 / NEW652 medium plug
Technical Specification

Maximum current carrying capacity of the decoder in sum


Rated continuous current output in sum


Continuous motor output current


Function output current

100mA each


CV 1
CV 17-18


Speed Steps (Selectable)

14, 28, 128


17 x 10 x 3.5mm

List of supported CVs
CV Name CV Default Description

Primary Address



Bits 0-6 contain an address with a value between 1 and 127. Bit seven must have a value of "0". If the value of Configuration Variable #1 is "00000000" then the decoder will go out of NMRA digital mode and convert to the alternate power source as defined by Configuration Variable #12.

Acceleration Rate



Determines the decoder's acceleration rate.The formula for the acceleration rate shall be equal to (the contents of CV#3*.896) /(number of speed steps in use).

Deceleration Rate



Determines a decoders braking rate.

Manufacturer Version No.



Manufacturer defined version info

Manufacturers ID



Values assigned by NMRA

EMF Feedback Cutout



Contains a value between 1 and 128 that indicates the speed step above which the back EMF motor control cuts off.

Extended Address


The Extended Address is the locomotives address when the decoder is set up for extended addressing (indicated by a value of "1" in bit location 5 of CV#29). CV#17 contains the most significant bits of the two byte address and must have a value between 11000000 and 11100111, inclusive, in order for this two byte address to be valid. CV 18 contains the least significant bits of the address and may contain any value.

Configuration Data #1


Decoder Configuration byte 1
Bit 0 = Locomotive Direction: "0" = normal, "1" = reversed.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.
Bit 1 = FL location: "0" = bit 4 in Speed and Direction instructions control FL, "1" = bit 4 in function group one instruction controls FL.
Bit 2 = Power Source Conversion: "0" = NMRA Digital Only, "1" = Power Source Conversion Enabled.
Bit 5 = "0" = one byte addressing, "1" = two byte addressing (also known as extended addressing).

All the CVs shown can be programmed in Operating Mode, Register CV Mode, Paged CV Mode and Direct CV Mode. All the CVs shown can be interrogated in all service modes. The Hornby Decoder supports programming on the Main. Some advice on the current draw of the decoder output: The current for all the decoder outputs is supplied by an internal rectifier with a maximum current of 1 Amp and the rated continuous current is 500mA.The sum of all currents to the motor and the function outputs should not exceed 500mA at normal continuous operation and cannot exceed 1 Amp. If the motor current exceeds 500mA the decoder will automatically cut off power to the motor. Function outputs are not protected. Each individual output can only draw up to it’s limit. For example if a motor requires as much as 400mA continuously then the function outputs combined should not exceed 100mA. Therefore, if the directional headlights require 50mA then the load Function 1 and Function 2 should not exceed 50mA.