With Hexadecimal (Hex for short) programming, there are two ways to calculate it. The first way is similar to doing it in Decimal. We'll show this method so you can see the relation. But adding things up in Hex is more cumbersome than adding them up in Decimal (simply because we don't have 16 fingers and are not use to that system). However, calculating each Hex digit individually (our second way to do it) is much easier than decimal. While explaining the second way is a bit more complicated, doing it is so simple you can quickly calculate any CV value in your head - once you learn the trick. We'll cover that last.

Each item that is controlled in a CV has a value. It's as simple as adding up the values for the features you want turned on and programming that value into the CV.

CVs are made up of eight bits, numbered zero through seven (0-7). Each of these bits has a value, starting with bit zero (0) having a value of one (1). Each subsequent bits value is double that of the one preceding it. Bit 1 has a value of 2, bit two has a value of 4, bit 3 has a value of 8, and so on. However, once you get past bit 3, Hex is a little different than the counting you're familiar with.

Yes, in hexadecimal 10 (one zero) is twice as much as 8 (zero eight) - you'll find out why later.

If you program a zero into the CV, all bits are turned off. If you add up all the values, you'll find that there's a total value of FF. Programming FF into the CV turns all the bits on. What's FF?

Well, in decimal counting, it goes from 0 through 9 before it rolls over to 10. When adding up a column of figures we call it "carrying the 1" . When counting in Hex, it goes from 0 through 15 before it rolls over to 10.

In fact, in Hex, any digit greater than 9 is not called what it is called in decimal - instead, we use letters: A = decimal 10, B = decimal 11, and so on though F = decimal 15. Just think of A through F as a third hand with six more fingers.

So when counting your fingers you would count 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F. Now you carry the one and start over with 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E, and 1F. It then rolls over to 20, 21, and so on all the way to FF. By the way, Hex FF is equivalent to decimal 255.

Since all other bits must be left off, the only two bits to turn on are 1 and 5. The value for bit 1 is 02 and the value for bit 5 is 20. Notice that this example is exactly the same as presented for the Decimal explanation of CV29. The only difference is that the value of bit 5 in decimal was 32, whereas here it's Hex 20. So, add 20 and 02 together to get Hex 22 (two two) to program into CV29.

Simple enough.

However, some values can involve adding numbers together that exceed 9 (especially with SoundTraxx sound decoders) to a point of not being able to calculate it in your head. We'll do one here first, then present another method that will be so simple you'll slap your head and say "duh".

CV51 in Throttle Up!'s DSD-150 Steam SoundTraxx decoder is for Background Sound Configuration. Each bit controls something different, as shown below.

Bits and Features

For arguments sake, lets say;

We want Real time off
We want Air pump on
We want the Blower enabled
We want Fireman Fred enabled
We want the Grease gun enabled
We want the Boiler pop value disabled
We want Automatic Blow Down enabled
Since we want all of these enabled things to work, we have to enable bit 7.

With all bits needing to be enabled except for bits zero (0) and five (5), we have to add them all up except zero and five. This means we have to add 02 + 04 + 08 + 10 + 40 + 80 for a total of DE. So how do you do that? The first thing to remember is that when adding up digits that are greater than 9, don't forget the letter digits. Let's present it in a format that's easier to see:

02 (zero two)
04 (zero four)
08 (zero eight)
10 (one zero)
40 (four zero)
80 (eight zero)

Now add them together. Yeah, right... From this standpoint, it's hard to see how adding that in your head can possibly be easy - but it is when you know the trick.

Don't look at it as adding a column of numbers and adding them ALL together like you have to do in decimal. Just add one digit at a time. Note that all values for bits 4-7 end with zero (0) - that's the key.

Hexadecimal numbers programmed into a CVs are ALWAYS two digits: a right and a left. Bits 0-3 make up the right digit, bits 4-7 make up the left digit. Just add them up individually and put them together to make the two-digit value. But don't add them, count them.

For example, with our bits 0-3 example here, we have 2 + 4 + 8. Start with the highest value first and count the smaller ones in. Adding 4 to 8, you count starting with 8, then say 9, A, B, C. We just added four to 8. Now starting with C, add two more by counting D, E. We now know that the right digit is E. Doing it this way you never have to count past F.

Let's do the left digit.

In our example, we needed to add 10 + 40 + 80. Ignore the zeros, as is already done in the illustration above, and simply add those numbers (1 + 4 + 8). Starting with 8, count four more into it the same way we did above - 9, A, B, C. Now add one more, D. Our left digit is D.

Combine the left and right digits together to make DE. Personally, I add up the left digit first, then the right. It doesn't matter. Do it whichever way is easiest for you.

Here's another tip:

When looking in Throttle Up! technical manuals for SoundTraxx sound decoders, you'll find that they provide a listing of what each bit does at the top of the page, as we saw in the illustration above. All you have to do is write the bit values in or under each box and scribe a heavy line down the middle, as shown below.