Configuration Variables (CV)

Note

CV.h contains default values for every CV. When your board is still “factory new” these values are automatically written into flash. CV_65 == 255 indicates a factory condition and resets all CVs to default.
Index 0 in the CV array corresponds with CV_1, index 1 corresponds with CV_2 and so forth.

Reset all CVs

To reset all CVs to default, a value of 8 can be written to CV8. Alternatively write a value of 255 to CV_65 this will also reset all CVs to default, but only after power cycling the decoder.

Speed step configuration

\(v_{min} = CV_{2}\)
\(v_{mid} = 16 \cdot CV_{6}\)
\(v_{max} = 16 \cdot CV_{5}\)

The figure above shows how the speed steps can be configured using the corresponding CVs. The red * represents \(v_{min}\) which is always at speed step 1, the green * shows \(v_{mid}\) at speed step 63, and the blue * shows \(v_{max}\) at speed step 126.

CV List

\(CV_{1}\) - Basic address

Short DCC address

\(CV_{2}\) - \(v_{min}\)

Min motor voltage/speed is: \(v_{min} = CV_{2}\)

\(CV_{3}\) - Acceleration rate

The time for one discrete acceleration time step can be calculated as \(CV_{3} \cdot CV_{175}\).

Note

Base speed steps are always 128/126 steps.

\(CV_{4}\) - Deceleration rate

The time for one discrete deceleration time step can be calculated as \(CV_{4} \cdot CV_{175}\).

Note

Base speed steps are always 128/126 steps.

\(CV_{5}\) - \(v_{max}\)

Max motor voltage/speed is calculated as: \(v_{max} = 16 \cdot CV_{5}\)

\(CV_{6}\) - \(v_{mid}\)

Mid motor voltage/speed is calculated as: \(v_{mid} = 16 \cdot CV_{6}\)

\(CV_{7}\) - Version No. (Read-Only)

Writing a value of 7 triggers an ADC offset adjustment.

\(CV_{8}\) - Manufacturer (Read-Only)

Default = 13 = Public Domain & Do-It-Yourself Decoders

Even though \(CV_{8}\) is defined as a Read-only CV, writing a value of 8 resets all CV values to the default values in CV.h.

\(CV_{9}\) - Motor PWM Frequency

\(f_{PWM_{MOTOR}} = (CV_9 \cdot 100 + 10000) \, Hz\)

\(CV_{11}\) - Packet timeout

If no package is received for \(x = CV_{11}\) seconds the decoder will automatically stop the motor (Emergency Stop).

\(CV_{12}\) - Permitted operating modes

Currently, DCC Digital mode is the only supported mode.

\(CV_{17}\) & \(CV_{18}\) - 14-Bit extended/long address

Address is only used if bit5 of \(CV_{29}\) has a value of 1.

Bit15 and bit14 which correspond to bit7 and bit6 of \(CV_{17}\) are always 1. \(CV_{17} = 192\) & \(CV_{18} = 0\) is also not a valid address. Otherwise, the valid value range of \(CV_{17}\) ranges from 192 to 231 and 0 to 255 for \(CV_{18}\) respectively.

\(CV_{29}\) - Decoder Configuration

Bit0 is can be used to reverse motor direction, i.e., 0 = normal, 1 = reverse. Bit5 switches between basic and extended addressing modes, i.e., 0 = basic address, 1 = extended address. The other 6 bits are currently not in use and therefore irrelevant.

\(CV_{31}\) & \(CV_{32}\) - Extended CV pointer (Read-Only)

Not in use.

\(CV_{116}\) to \(CV_{171}\) - PWM Slice configuration

Every slice controls two independent output channels, duty cycle from 0% to 100% inclusive, and can be configured with several parameters:

Wrap (16Bit): Sets the slice time period of x cycles - effectively determining the frequency
Clock Divider: Additional clock divider
Level Channel A / Level Channel B (16Bit each): Determining how many of the x cycles the signal is at a high level - effectively determining the duty cycle

To see which CVs correspond to which slice and channel, it is advisable to use CV.h as a reference.

The PWM frequency is calculated as follows: \(f_{PWM} = \frac{125 \, \text{MHz}}{(CV_{\text{clk_div}} + 1) \cdot (CV_{\text{wrap}} + 1)}\)

The duty-cycle can be calculated as follows: \(D = \frac{CV_{\text{Level}}}{CV_{\text{wrap}} + 1}\)

A more detailed explanation regarding PWM can be found in the RP2040-Datasheet - Chapter 4.5.