# KB305: Programming CV17 & CV18 (four digit addresses) manually

This article was last updated on Oct. 17, 2010, 2:52 p.m. | Print Article | Leave Feedback

Some DCC systems need to have CV's 17 and 18 programmed separately to assign the decoder a 4 digit address.

Digitrax command stations handle this automatically by default.  If you have a decoder that needs manual entry of CV17 & CV18, follow these steps:

You cannot simply split the four digit address in 2 halves and input these into CVs 17 and 18. A conversion from decimal numbers to hexadecimal numbers is required. Once the hexadecimal conversion for the 4 digit address is performed, this number is then split in half and then each half is input into CV17 and CV18 respectively.

To perform this operation you need a scientific calculator or the calculator accessory on your computer, make sure your p.c. calculator is set for the scientific mode.  A Google search using the terms "DCC hexadecimal conversion" will turn up several different online decimal to hex converters.

The Calculation

For example let's say your 4 digit address is 1998.  Add 1998 to 49152, which equals 51150, [1998+49152=51150].

Under the DEC(decimal) setting on the calculator, input the result (in our example, number 51150).

Then change the setting to HEX(hexadecimal).  You will get a hexadecimal number (in our example, C7CE, 51150 decimal equals C7CE hex).

Split the resulting number into the first two digits and the last two digits, which gives you 2 separate hex numbers for CVs 17 and 18.

In our example, the value C7 goes into CV17, and the value CE goes into CV18, but first you have to convert these 2 numbers back into decimal values to input them into the CV's.

Enter the first two hex digits into the calculator using HEX mode.  Then change the calculator to decimal mode to derive the decimal number to enter into CV17.  In our example, enter C7 into the calculator using HEX mode, then switch the calculator's setting back to decimal, you will get the number 199; C7 [in hex]=199 [in decimal].  Input the value of 199 into CV17.

Enter the last two hex digits into the calculator using HEX mode.  Then change the calculator to decimal mode to derive the decimal number to enter into CV18. In our example, enter CE into the calculator under the Hex mode, then switch the calculator's setting back to decimal, you will get the number 206; CE [hex]=206 [decimal]. Input the value of 206 into CV18.

In our example, this procedure programs the decoder a 4 digit address of 1998.

Set CV29 to activate the 4-digit address

The next step is to go to CV29 and program it to use the 4 digit address.  There are many choices depending on the loco characteristics you want to use.  The most common setting for CV29 is 34.  This CV value tells the decoder to use the 4 digit address, analog mode conversion disabled, 28/128 speed steps, and normal direction of travel set to forward.