First steps in programming and changing C.V.s

By Keith Waddell

• If you have ever had the following problems (and I have

seen this at the club…) :-

• “when I turn the throttle on my loco to speed step 1, the loco drives

forward at 40mph!!!”

• “my loco is too loud – it drowns out the conversation in the corner”

• “my loco is too soft, how do I turn the volume up?”

• “how do I know the address my loco is?”

• “my two identical locos are not speed matched, how do I fix that?”

• “my loco doesn’t move at the same speed in forward as it does in

reverse”

• “how do I program realistic braking and acceleration?”

• No

• But It does work like a fax machine or when you log onto the internet

• Tiny digital pulses are overlaid on a permanent AC voltage which is around 16V (remember DC is variable between 0-12V)

• These pulses allow the hand throttle to communicate via the main control box with the loco decoder.

• Handshake pulses backwards and forwards allow the right commands to be sent to the right loco

• Configuration Variables. Each is a register that store a

particular command.

• They have two parts, the first is the CV number and sets

the correct decoder register

• The second is the value that you wish to operate at.

CV 2

Value 8

• 255 on most older sound decoders, although most new

ones now go up over 400

• 16 on early Bachman decoders

• NMRA has reserved up to 1024 - a lot for future use

• Of course

• No seriously, you really only need to know a few – at

least to start with …… baby steps….

• Use the Readback feature on the controller to readback

what has already been programmed into the loco

• Read back all the CVs you are likely to change and make

a note of them.

• Why?

• In case you screw up – its easy to plant the wrong value

in the wrong CV.

• Yes

• Why? Because the manufacturers although guided by NMRA directions, have decided to go their own way in certain controls – for instance with sound volume!

• If you do not know the decoder type and you do not have a manual then you need to do some research.

• One way is to look up what the CV value of CV8 is – manufacturer ID

• Another is to look for any paperwork that came with the loco

• Another is to take the top off the loco and look at the decoder board itself.

• As long as you know the decoder type you should be ok

• Although you may not know the precise type of decoder,

as long as you know the manufacturer you should be

able to program most things

• Go to the web and download the specific manufacturers

decoder manual. (Most new locos are only delivered with

a cursory manual anyway and most new decoders are

only delivered with a brief manual).

• Print the manual out. Yes I know it might be 64 pages….

• MRC – The club gets a special discount – budget priced

• MTH – Top end and only in MTH locos

• Bachmann – budget priced, early ones limited

• QSI – robust sound, used to be in early Walthers, Broadway

• TCS- Bill’s favorite especially with the WOW sound, goof proof warranty

• Soundtraxx- popular in Athearn, Walthers. Early tsumanis have annoying bugs. Responsive tech support

• Digitrax – good non sound, early sound primitive

• ESU Loksound - popular in Europe and now used in a lot of US locos. Responsive tech support (Keiths favorite)

• NCE – non sound. Budget priced and very good

• You must keep records

• I use a two part approach

• First part: I have a record card for each loco. On this record card I write the loco manufacturer, the decoder manufacturer, the loco road number, the loco address, what each of the functions do and their numbers and common CVs that I have altered. I also add whether the loco has been speed matched with other locos and which ones

• Second part: I have a record sheet together with the original manufacturer directions/ manual in a clear plastic folder. One folder per loco and these are kept in a binder.

• Can I do all this on a PC/ipad/iphone. Yes but it must be accessible quickly. - In the “Heat of battle”, I prefer a written record.

• First make sure you are on the programming track.

Press Prog

Pressing Prog

Toggles between Prog

Track, Program on main

and Readback

To select one then press

enter

Asks for address, if read back

press enter again

Says read then you hear loco

chuntering or clicking

Displays shows loco address

Now press shift key

Shows SV ---

Press enter

Says read and chunters

Now displays SV entry (start voltage)

Press shift

Now says ACC ---

Press enter

Now displays ACC or acceleration value

Similarly

Press shift

Now says dec---

Press enter

Now displays dec or decelleration value

Press shift

Now says TV---

Press enter

Now displays TV or top voltage value

Press shift

Now displays CV ---

Now enter a value. Say 6 (mid pt)

Press enter

Now displays the CV value in CV register 6

Press shift

Goes to another CV entry, enter another CV number

say 5 (same as TV)

Press enter

Displays data in CV5

To exit : press prog again or another key like loco

• This answers the question “how do I know the address my

loco is?”

• Loco address – if you program with a two digit address then

CV1 is used - most of you want a 4 figure address as there are

so many locos – in this case CV 17 and 18 are used but only

after CV29 has been changed – “HUH?!!!”

• Fortunately for most of you this is all done for you by the DCC

controller – you just type the address you want when ADD

comes up on the display on the MRC unit.

• “Is he going to mention CV29 again cos I’m going to need an

aspirin…”

• Much later and for most of you, you need not worry about it

• To read back the loco address go to read back mode on

a programming track

• Press enter

• The display will flicker, you will hear or see the loco

flicker, shudder or move slightly

• The display will show the loco address

• To enter a new address, go to program mode (program

track or main), press enter, (if main then the system will

show the old address then press enter) and enter in the

new address.

• This answers the question “when I turn the throttle on my loco

to speed step 1, the loco drives forward at 40mph!!!”

• In a way it is best to consider this CV together with CV 5

and 6 and I will explain why with a diagram.

• Just to let you know that manufacturers have designed

their controllers to easily enter CV 2 and 5 via the Start

and Top speed setting

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Graph of CV setting vs input speed

Speed(in bits out of 255)

CV 2 – start voltage set to say 3

CV6 – mid pt for speed set to say 80

CV5 – top speed set to highest level of 255

Speed step 28/28

Speed step 14/28

Speed step 1/28

• The manufacturers defaults are typically 0,1,2,3 and

sometimes 10

• The ideal CV2 value is one that “just” gets the loco

moving when the loco is set to speed step 1 when using

24 speed steps.

• Sometimes it is more prototypical to “just” have a diesel

loco not moving at speed step 1 especially if you have a

sound decoder. Why? Because the engine will rev up

before it moves.

• Obviously this wont work for a steam loco – chuffs will

start without movement – not good.

• The initial resistance of the motor to move.

• The inertial resistance in the gearbox

• The resistance in the running wheels

• The weight of the loco

• Whether back emf is in use by the decoder – more later.

• Good : MTH, Walthers, Broadway Ltd, Mahanu, locos

with “can” style motors.

• Bad : Old Athearns, any locos with heavy looking

gearboxes – some brass, old style 3 pole motors. Locos

with extensive gear mechanisms – shays etc.

• CV 5 or the top speed are usually set at 255 or 128

depending on the manufacturer – a setting of 255 usually

gives a motor input of 12V – same as an analogue DC

system.

• CV6 or the mid pt – the setting at speed step 14 (out of

28) are usually half that of the top speed – 128 or 64

respectively. Some manufacturers may drop this down a

bit as default to allow for better slow speed control.

• The loco gearing

• The motor speed

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

Switcher

Mainline Loco

From suggestions in

the Digitrax manual

1 14 28

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

Speed adjusts slowly at low

speed, but when speed gets

over speed step 14/28, the

loco accelerates much faster.

This means fine control in a

yard, while giving more

prototypical top speed out on

the main.

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

This was Bob’s articulated loco

until we changed CV2. The

engine went from 0 mph to

40mph at speed step 1

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

This is the approx graph

for the clubs Sante Fe F

units. I would estimate

the top speed at well

over 100mph, and it gets

there pretty quick on the

throttle

• CV2, the start voltage needs to be set to a number that is

just enough to get the loco moving at speed step 1/28

• CV5, the top speed (speed step 28/28) needs to be set to

what the loco might be capable of in a prototypical

setting. For a switcher say 40mph, for a road switcher

60mph and for a mainline loco 90mph.

• CV6 – mid pt (speed step 14/28), in my view should be

set to a value that allows good slow speed control in a

yard, say 15mph for a switcher or 20mph for a main line

loco.

• HO is 1 in 87

• That means a loco travelling at 10mph in real life will travel at 10/87 miles in one hour at scale.

• 60mph is equivalent of 88ft/sec

• So 10mph is 10x88/60x87ft/sec at scale

• So 10mph is 1/6th of 1 ft/sec or 2inches/sec

• If you count out loud slowly (e.g. “And one and two and three and four and five and six” this gives you an approx 6 second interval)

• 1 ft is the length of a 6ft guys shoe.

• Just measure the distance the loco goes in 6 seconds in ft, multiply by 10 and you have mph.

10mph

30mph

60mph

1 ft in 6 secs

3 ft in 6 secs

6 ft in 6 secs or 1 ft in 1 sec

• I have adjusted the start voltage and the top speed but

the speed doesn’t change through speed step 14/28. – its

likely that the CV6 mid pt has not been altered.

• Altering CV5 and 6 changes nothing – its likely that the

decoder is operating in speed table mode or preset

speed table mode- this is more advanced and will be

covered later – this will involve CV29 – oh no where’s the

aspirin….

• This applies to sound decoder locos only

• At this point it is critical that you access the decoders

manual.

• Why? Because different manufacturers have used

different CV values for their master volumes…. Groan…

• This answers the question -“my loco is too loud – it

drowns out the conversation in the corner” or “my loco is

too soft, how do I turn the volume up?”

• ESU loksound use CV 63.

• Soundtraxx use CV 128

• 1. Read back the current value. This requires going to the programming track, go to Read back mode, enter CV 63 or 128 or whatever and press enter.

• 2. Make a note on a record card of that entry.

• 3. Go to operate mode on the controller and turn the sound on – idle mode is fine for diesels, for steam use rolling wheels and speed step 4 to get the chuff noise.

• 4. Now ideally go to program on the main mode.

• 5. Go to CV 63 or 128 and change the value – half or double.

• 6. Listen. Then change the CV accordingly based on personal preference. Iterate 4 through 6 until ideal volume.

• 7. Enter the new CV 63 or 128 value onto yr record card ( I put a line through the old value and enter the new value – its nice to know where you came from…)

• Consult yr manual.

• For example if you have a Loksound decoder and you

want to up the whistle noise on a steamer then adjust CV

275 (the default is typically the max level of 128 so you

may have to up the master volume and lower the other

sounds). If you have a soundtraxx decoder then you will

be adjusting CV129 to a max of 255.

• AGAIN PLEASE CONSULT THE MANUAL!! DO NOT

ASSUME THAT Loksound CVs will work in the same way

on say a Soundtraxx decoder and vice versa.

• This section will answer the question “how do I program realistic braking and acceleration?”

• Of course the easy way to increase and decrease speed in a realistic way is to work the throttle slowly, climbing up through the speed steps gradually. However this not really realistic. It is perfectly possible on the prototype to a put a diesel in notch 8 from rest and watch the loco slowly accelerate a heavy train to full speed over the next scale mile without further throttle input. Similarly when braking a heavy train, the throttle is shut back to notch 0 and the brakes applied and then you watch the train decelerate over the next ½ mile to zero mph.

• So how do we mirror this in model terms?

• In CVs 3 and 4 (ACC and DEC when going through the MRC

controller in program mode) we have the ability to enter

momentum values to give that prototype lag on being able to

accelerate and decelerate.

• CV3 entry is the Acceleration and CV 4 the braking.

• The typical values for most new locos out of the box are 10 or

20 for both modes.

• Some manufacturers such as Loksound actually allow you to

enter a value based on time to reach said throttle speed. For

example a CV3 entry of 32 will mean that the train will

accelerate from zero to say a throttle setting of 14 in 32 x 0.25

secs or 8 secs. It is similar for the deceleration value in CV4.

• How heavy the train is? If the loco is going to pull a heavy train then you may want to increase the momentum substantially – a lot of this will depend on whether the loco has been compensated for by “back emf” – a facility for keeping speed up under load.

• How jerky is the acceleration and deceleration of the individual loco with a zero momentum. If the loco suddenly jerks from one speed to another and it doesn’t look real then you may want to add momentum into CV3 and 4.

• Typically momentum is great for mainline use but a real pain for yard work- you can easily overshoot a coupling point with too much momentum. - Maybe Tony sets up the locos used in the operations group with momentum to test you guys out….

• Play with parameters and see what works for you

• This section answers the question :- “my two identical locos

are not speed matched, how do I fix that?”

• This can be a time sink so be warned

• The most usual case use of speed matching locos is so

they can operate in a consist.

• To do this successfully you will need to operate and

program on the Main (otherwise if will take forever to

adjust the speeds- although you can do it by shuttling

between program and operate modes)

• The other ideal set up is to use a circular piece of track

so the locos can go round and around

• The locos do NOT have to be matched that precisely.

• Why?

• When pulling a load it tends to even out slight

discrepancies although watch for one of the locos to slip

(usually you hear this via a chuntering noise).

• Check to see whether the locos are responsive to

changes on CV2,5 and 6. If they are set up for speed

tables then it will be aspirin time….

• Some old athearns require “warming” up – this is a pain

as the locos are either synced cold or hot but not both.

Maybe time to re motor

1

2

For diesels, its best to run them in the direction that they will

normally run in a consist – i.e. back to back

• Start each loco at speed step one.

• Do they creep along at the same speed? (sometimes to

check this arrange the locos so that they are only a 1-2 ft

apart)

• If no then adjust one of the locos (say loco 1) CV2.

• Be careful here, I have seen a few locos that will not

budge no matter what you put in CV2 – in this case you

will have to face the fact that speed step 1 will not move

either loco – adjust the other loco instead so that it

doesn’t move at speed step 1.

• Now set the speed step to 14

• Are the locos going at the same speed?

• This is where the circular track comes in handy – is one

loco catching the other up?

• Now adjust CV6 on one of the locos such that they

appear to run at the same speed

• I think at this point you will start to understand why

running in “programming on the main” mode is better –

the CV can be changed on the fly and the effect seen

instantly

• Now set the speed to full (speed step 28)

• Are the locos going at the same speed? (are they still on the track??? – if too fast then back off to speed step 21)

• Now adjust CV 5 (top speed) on one of the locos – the same one as for the other settings, obviously…

• Now go back and check the full range of speeds to see if they match up.

• Typically I find that one loco lags a bit behind the other – for instance at speed step 8 both are the same then at step 9 one steps out ahead then at step 10 they are back in sync again. The difference is typically small and under load will not be noticeable.

• So your loco should go the same speed in both directions?

• Wrong. Its rare that a loco will go in exactly the same speed in one direction when compared to the other. However the difference is usually small so only attempt adjustment if you detect “chuntering”

• Try yr locos first. Repeat the previous three steps – speed step 1, 14 and 28 but this time with the locos in reverse and do not adjust any cvs. Just observe.

• If they match – good, if not then go to yr decoder manual (one of them) and hunt out the section that is labelled “Reverse Trim”

• On Loksound and Soundtraxx decoders, the reverse trim is CV95. It is not on every decoder.

• Might be worth taking the locos off onto a programming track and reading back each CV95, making a note then put them back on the main.

• A value of 0 in CV95 means that there is no “trim” between forwards and backwards.

• A value of say 128 is the factor used to multiply the motor voltage when driving forward.

• Now pick a loco to adjust and change CV95 “on the fly” for that loco and see whether it makes a difference at speed step 14. I typically adjust the value by the same ratio that I see in the speed difference.

• Once tested in reverse then go back and try speed steps 14 in forward mode again.

• Well we have answered the last question of “my loco doesn’t move at

the same speed in forward as it does in reverse”

• I will try and cover speed tables at a future time – worth doing

because a number of manufacturers default to preset exponential

tables see example below – however this will mean adjusting CV29 –

bring aspirin…

0

50

100

150

200

250

300

0 20 40 60 80 100

Graph of CV vs actual speed

Speed(in bits out of255)

• Advanced Speed tables and CV29

• Lighting

• Consisting

• Back emf

• Chuff rate