SoundTraxx SoundCar Users Guide - Manual (Page 10)

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
Tsunami SoundCar User’s Guide Page 6
127 converts to a simple 7F in hex. If your command station’s interface allows
a limited number of digits, hex numbering can allow your cab to display a
greater range of numbers.
Binary – Binary numbers get their name from the fact that they only use two
digits, 0 and 1, which are called “bits.” Binary is the fundamental numbering
system used by computers, including those found inside a digital decoder.
Because there are only two bit values, more digits are required to represent
a number when using binary. For example, the decimal number 127 is written
as 01111111 in binary notation. A “byte” is a binary number made up of eight
bits, and a “nibble” is one‑half of one byte, or four bits.
Each CV is made up of one byte (i.e., eight bits) and can store any number
from 0 to 255. Most CVs contain a single piece of data that can be easily
represented in any of the three number formats described above. For
example, CV 3 (Baseline Acceleration Rate) can be loaded with any value
from 0 to 255 and it will always and only affect one thing – the acceleration.
Now, a little more about those bits: Some CVs use the individual bits to
control various features. This keeps the number of CVs more manageable
and allows up to eight distinct features to be controlled using a single CV. Bit
variables require binary input and will only respond to input values of 0 and
1. For this reason, programming by the bits is usually reserved for simple
variables that are either ON or OFF, disabled or enabled, etc. Unfortunately,
bit variables are difficult to represent in any form other than binary while still
preserving their meaning. As most DCC system user interfaces don’t use
binary representation, programming by the bits using binary requires a little
bit of math (just simple addition though!) to convert values into the decimal or
hex representations used by most DCC systems.
To facilitate programming, we have tried to use decimal representation in this
manual when defining advisable values to program into a given CV; however,
you will occasionally find binary values listed in the Tsunami SoundCar
Technical Reference.
Now, let’s try a programming example for CV 29 (Configuration Register 1),
which works best when programmed by the bits. When programming
individual bits, we suggest the following procedure to determine the correct
decimal value. Referring to the CV description in the Tsunami SoundCar
Technical Reference, write down the value that will produce the desired
response for each bit. In this example, we want to program this CV so that
speed tables and 28 speed‑step mode are enabled. As indicated in the
technical reference, bits 1 and 4 should both be set to 1 to enable the desired
features, with all of the other bits set to 0. Write down the individual bit
values as shown below:
Basics of Programming