SoundTraxx DSD-150/DSX Owners Manual - Manual (Page 19)

Digital Sound Decoder Owner's Manual 19
After awhile, you will probably want to make some changes such as selecting a new address or changing a sound
effect. The following paragraphs break the DSD’s CVs into various subsystems so it is only necessary to change a
few CV’s at a time. As you become comfortable with the DSD’s operation, move onto a new section and begin
exploring the options and capabilities found there. Detailed information on any CV can be found in the DSD Techni-
cal Reference located in Part II of this manual.
Bits and Bytes
One of the most confusing aspects of programming a CV is figuring out what the all the different bits, bytes and x’s
found on the various decoder manuals (including this one) mean. The problem is compounded further by differences
in each command station manufacturer’s user interface. For those users unfamiliar with such terms, a short math
lesson (ugh!) is in order before proceeding:
Each decoder CV stores a numeric value that can be represented in one of three forms:
Decimal - This is the form we are all familiar with and use in our day-to-day lives. Numbers are represented
as a sequence of digits composed of the numerals 0,1,2,3,4,5,6,7,8, and 9.
Hexadecimal - Also referred to as simply “hex”, this is a more specialized number representation that, in
addition to 0 through 9, also uses the characters A-F. It has the advantage that a given decimal number can
be more compactly represented. For example, the decimal number 127 is simply 7F in hex (one less digit).
This allows user interfaces with a limited number of digits to display a wider range of numbers.
Binary - Binary numbers get their name from the fact they use only two digits 0 and 1 called ‘ bits’ and is the
fundamental number system used by all computers including the ones found inside a digital decoder. Be-
cause there are only two bit values, it takes more digits to represent a number using binary. The decimal
number 127, for example, is written as 01111111 in binary notation. A ‘
byte’ is a binary number made up of
eight bits. And a ‘ nibble’ is half a byte or four bits. Really! We didn’t make that up.
Coincidentally, each CV is made up from one byte or eight bits and can store any number between 0 and 255. Most
of the CVs contain a single piece of data that can be easily represented in any of the three forms. i.e., CV 3, the
acceleration rate, can be loaded with any value from 0 to 255 and it always affects the same thing - the acceleration
rate.
On the other hand, some CVs use individual bits to represent different variables. This allows a CV to hold up to eight
individual variables within a single byte and is done in order to conserve the numbers of CVs. As the bit variables can
take on only one of two values 0 and 1 they are usually used for simple variables that are either On or Off, enabled
or disabled or something similar. Unfortunately, bit variables are difficult to represent in any form other than binary
and still preserve any meaning. Because most DCC system user interfaces don’t use binary representation, these
numbers are the most difficult to work with and require a tedious series of additions to convert to the decimal or hex
form used by most systems.
Whenever possible, we have tried to use the decimal number system in this manual when describing the proper
values to program into a given CV. For users of those systems that use hexadecimal numbers, we have shown the
hex equivalent in parenthesis. Throughout this manual, a hex number can be distinguished from a decimal number by
noting a 0x prefix. Thus 0x10 is the hex version of sixteen and not ten as one might guess. Binary numbers are
represented using a ‘b’ suffix. 100b is thus the number four and not one hundred.
To further assist the math-impaired user, we have provided a handy-dandy conversion table in Appendix C that
allows one to quickly convert between decimal, hex and binary.
When working with bit variables such as CV 29, we suggest the following procedure for determining the correct value
to program. Referring to the CV description, write down from left to right, the value of each individual bit. Consider for
example, the case of CV 29. We would like to set this CV so the speed tables are enabled and the 28 speed step
mode is in effect. Referring to page 21 in the DSD Technical Reference, we see that bit 4 and bit 1 should be set to
1 and all other bits are cleared to 0. Starting with bit 7 and working to the right, we write down the individual bit values
and get: