TinyFuncDecoder v1.0

What is a Function Decoder?

A DCC decoder is a tiny PCB with a MicroController used for model railroads. It gets DCC messages over the track, interprets them as commands and executes these.
There are motor (or loco) decoders, function decoders and accessory decoders. Motor and function decoders are mostly the same, but a function decoder can more or less only control simple on/off outputs. Motor decoders have also an H-bridge to fully control a DC motor in both directions. Accessory decoders are for controlling switches, crossings and so on. (On our model railroad they are controlled over our own RailBus-Controlling-Network. (More on that topic later.))

Why I built my own function decoder:

You can get motor decoders for 20€ and more. (For 20€ you get a simple decoder: 1 motor & 2-4 function ouputs)
Function decoders start also at 20€. Then you get also 2-4 function outputs. But no motor output. So: What is the benefit to buy a function decoder if you can get a full loco decoder for the same price?? And if I built it myself: The costs will reduce down to 3-5€ (if it goes well…^^)

Plus: I can program all the functionalities which I want to have. And there are some of them, which are not provided by bigger manufaturers!

The functionalities

4 Outputs à max 100mA
Full possibility to map all 29 functions to all outputs (maybe there will be 69 functions in future, but I don't need them now, so they are not fully implemented yet.)
8 Output effects: 0ff, full brightness, dimmed brightness, 2 distinct blink patterns, fade in/out (and 180° phase shifted), apply the current velocity as PWM to the output
Default ouput effects for every output and direction
128 Bytes of storage for your own program: Which function will turn effect on which output? Shall output 2 only on, if F3 AND F4 are activated? And off again if F5 is on? (And so on…)
NMRA decoder lock: you can run up to 256 decoders listening to the same address (not distinguishable on main track. But you can select them by decoder lock id on programming track.)
Subaddresses: You can run up to 65536 decoders with the same address on main track! F13-F28 will be used to select the decoder. They will only react if their subaddress is set!
Listening to other addresses: In this mode they can listen to other addresses, too! You don't need to save a driving trailer and every loco as consist pairs. You just say: "Hey trailer: Listen also to this loco, now!"
~~Analog modus: Saves the current active functions and apply them also on analog tracks.~~ (Not implemented yet)
Maybe consist addresses work (I don't need them, but this will be checked later.)

Hardware

Overview
Load has to be connected between decoder + and the respective output.
It is strongly recommended to install a capacitor between decoder + and decoder – !!!

Modes

As normal function decoder

Nothing special happens: You can map all 29 functions to all 4 outputs.

Subaddresses are activated

You can save the subaddress to CV 31 and 32. (#31 high, #32 low byte.) To access the desired decoder, do the following:

Make sure that F12 is off while setting F28 to F13.
Select the subaddress with F28-13 (F28 is msb, F13 is lsb; F28 = 32768,… F20 = 128,… F14 = 2, F13 = 1).
Wait 1-2 seconds to ensure, that these function settings are read by every decoder with the same main address.
Turn on F12. Every decoder with this loco address and the selected subaddress will now listen to F0 - F11.
After setting the functions, turn off F12 to don't accidentally apply unwanted function changes. Memo 1: If this mode is activated, you cannot use F12 - F28, because of their special functions now. Memo 2: This mode should not be activated with the listening-to-other-addresses-mode at the same time!

Listening to another address

In this mode you can set an address of another loco over the function buttons. The decoder will also react on messages sent to the loco.

To do this, set the desired address to function F26-13. (F26 is msb, F13 is lsb; F26 = 8192,… F20 = 128,… F14 = 2, F13 = 1).
F27 says if the other address is a short (0/off) or a long (1/on) address.
F28 can inverse the direction.
Set F12 to apply changes on F13-F28. Memo 1: If this mode is activated, you cannot use F12 - F28, because of their special functions now. Memo 2: This mode should not be activated with the subaddress-mode at the same time!

Effects

No	BIN	Name	Possible settings
0	0000	Off
1	0001	Full brightness	CV 68
2	0010	Dimmed brightness	CV 69
3	0011	Speed as PWM
4	0100	Blink pattern A	CV 71 - 75
5	0101	Blink pattern B	CV 76 - 80
6	0110	Fade in/out	CV 70
7	0111	Fade 180° phase shifted	CV 70

CV table

Bit numeration:
1 Byte has 8 bits: bit 7 is most significant bit (msb) =128, bit 0 is least significant bit (lsb) =1. (76543210)
bit 7: 128
bit 6: 64
bit 5: 32
bit 4: 16
bit 3: 8
bit 2: 4
bit 1: 2
bit 0: 1

CV	Description	Default value
1	Short address	3
7	Version	1
8	Manufactor ID (Write 8 for resetting the decoder)	13 = DIY
12	Outputs used for acknoledgment bit 0: Output 1 bit 1: Output 2 bit 2: Output 3 bit 3: Output 4	bit 0: 1 = 1 bit 1: 1 = 2 bit 2: 0 = 0 bit 3: 0 = 0 =1+2 = 3
15 & 16	Decoder Lock: CV 16: Decoder Lock Set distinct lock numbers for each decoder on one loco with the same decoder address (0 = motor, 1 = another decoder,…) CV 15: The key: Set CV15 to the loco on programming track and only that decoder where CV 15 equals CV 16 will apply on changes!	CV 15 = 0 CV 16 = 0
17 & 18	Long address	CV 17 = 0 CV 18 = 0
19	Consist address	(set automatically)
21	Consist address active for F1-8 bit 0: F1, …, bit 7: F8	0
22	Consist address active for FL,9-12 bit 0: FL_fwd, bit 1: FL_rev, bit 2: F9, …, bit 5: F12	0
28	~~BiDi Config~~	0 (not implemented yet)
29	bit 0: Direction inverted? (0= normal, 1= inverted) bit 1: Is 28 steps mode? (0= 14 steps, 1= 28 steps) ~~bit 2: Is analog enabled? (0= digital only, 1= analog enabled (saving last enabled functions)~~ bit 3: Can listen to other address? (0= acts like normal decoder, 1= can also react on messages to other decoders) bit 4: Using subaddress? (0= acts like a normal decoder, 1= using subaddresses) bit 5: Is my address a Long Address? (0= My address is short (CV1), 1= My address is long (CV 17&18)) bit 6: Are special effects enabled? (0= off, 1= on) bit 7: not used.	bit 0: 0 = 0 bit 1: 1 = 2 bit 2: 0 = 0 bit 3: 0 = 0 bit 4: 0 = 0 bit 5: 0 = 0 bit 6: 1 = 64 bit 7: 0 = 0 =0+2+0+0+0+64+0 = 66
31 & 32	If subaddress is used, this subaddress is stored here: CV 31: Subaddress high byte CV 32: Subaddress low byte Note: both CVs are also used to store the Other Address configuration! Here CV 31 stores F28 (in bit 7) down to F21 (in bit 0) and CV 32 stores F20 (in bit 7) down to F13 (in bit 0)	CV 31 = 0 CV 32 = 0
34-62	Function - Output - Mapping Which function activates which output? bit 0: Output 1 bit 1: Output 2 bit 2: Output 3 bit 3: Output 4 ~~bit 4: Output 5~~ F0: CV 34 … F28 : CV 62	CV 34 = 2+1 = 3 (F0 activates Output 1 and 2) CV 35-62 = 0
63-67	Output - Default Effect - Mapping Which effect shall be applied? bit 7 to 4: Forwards direction bit 3 to 0: reverse direction Output 1: CV 63 … Output 4: CV 66~~, Output 5: CV 67~~	CV 63: 0x20 = 0b 0010 0000 = 32 -> in Forward: Dimmed CV 64: 0x02 = 0b 0000 0010 = 2 -> in Reverse: Dimmed CV 65 - 67 = 0
	Effect settings
68	Brightness of full light (effect 1) (0-255)	255
69	Brightness of dimmed light (effect 2) (0-255)	50
70	Cycle time of fading (effect 6 & 7) in 10th of a second (0-255)	15 = 1.5 sec
71 - 80	On & off times for blink pattern A and B (effect 4 & 5) `order Blink A \| Blink B` `1 off-time 71 \| 76` `2 ON -time 72 \| 77` `3 off-time 73 \| 78` `4 ON -time 74 \| 79` `5 off-time 75 \| 80`	CV 71 = 0: no off at start CV 72 = 1: 0.1s on CV 73 = 1: 0.1s off CV 74 = 1: 0.1s on CV 75 = 10: 1s off CV 76 = 0: no off at start CV 77 = 2: 0.2s on CV 78 = 2: 0.2s off CV 79 = 2: 0.2s on CV 80 = 2: 0.2s off
118 - 128	Function memory for analog and subaddress mode.
129 - 255	Special Effects	see special effects programming chapter

Special Effects

This area contains lists of rules of effects, which shall be applied to outputs if a function is on. There are only 4 regulations in this area:

A rule has to start with the function number (combined with 2 flags. More on them later)
The rules have to be separated with a zero-value (0)
The last effect which is applied to an output is the final one. (ie: If an earlier effect says "Output 1 has to be dimmed on", but later it says "Output 1 has to be faded", the output will be faded!)
An output can only turned on, if it is activated by CV 34-62. (This is to allow AND-conjugations. ie: Ouput 2 can only be turned on if F5 AND F6 are on.)

We will see how it works, when we have a look to the default values:

The Brights (on F3)

CV 129: 195 In binary: 11 000011. (Separated in flags, function number)
The last 6 bits (000011 = 3) say: This rule is for function 3.
bit 7 = 1: This rule applies if F4 is active on my address. (The address of the decoder)
bit 6 = 1: This rule also applies if F4 is active on the other address, which the decoder is maybe listening to. (Only if other-address-mode is active)

CV 130: 18 In binary: 0 001 0010. (Separated in direction, effect, output mask)
bit 7 = 0: This is only for reverse direction
bit 6-4 = 001: Apply effect 1: full brightness
bit 3-0 = 0010: Apply this effect on output 2. (bit 0: Output 1, bit 1: Output 2, bit 2: Output 3, bit 3: Output 4)

CV 131: 145 In binary: 1 001 0001. (Separated in direction, effect, output mask)
bit 7 = 1: This is only for forward direction
bit 6-4 = 001: Apply effect 1: full brightness
bit 3-0 = 0001: Apply this effect on output 1. (bit 0: Output 1, bit 1: Output 2, bit 2: Output 3, bit 3: Output 4)

CV 132: 0
Separator: End of rule

Shunt (on F4)

CV 133: 196 = Which Func: 11 000100 => my ot F4
CV 134: 35 = Output: 0 010 0011 => in Reverse: Effect 2 on Output 1 and 2 (=Dimm on 1 & 2)
CV 135: 163 = Output: 1 010 0011 => in Forward: Effect 2 on Output 1 and 2 (=Dimm on 1 & 2)
CV 136: 0 = separator

Turn off cab 1 (with F5)

CV 137: 133 = 10 000101 => my F5
CV 138: 1 = 0 000 0001 => in Reverse: Effect 0 on Out 1 (Off on 1)
CV 139: 129 = 1 000 0001 => in Forward: Effect 0 on Out 1 (Off on 1)
CV 140: 0 = separator

Turn off cab 2 (with F6)

CV 141: 134 = 10 000110 => my F6
CV 142: 2 = 0 000 0010 => in Reverse: Effect 0 on Out 2 (Off on 2)
CV 143: 130 = 1 000 0010 => in Forward: Effect 0 on Out 2 (Off on 2)
CV 144: 0 = separator