academic Q about DMX packet protocol

  • Hello i'm just learning about DMX communication and i'm curious about what looks to me like a non sequitor in the design of the protocol. a slot value is defined as a single # from 0 - 255. the simplest slave device implementation, i presume, would consist of a circuit that uses the slot value to control the voltage (a PWM output) going to a light.

    it seems to me that, because of the redundancy of the protocol (meaning that a given device is often recieving the same number repeatedly), that it would be smart to designate a NULL value (either 0 or 255) that a slave device would ignore. certainly the engineers who designed the protocol thought of that and why did they not make it part of the specification?

    does anyone know about this?

    thanx, mike:)

  • Exactly there is no difference in


    Code
    if (newValue != null) over (newValue != oldValue)

    beside the fact that you need to spend 1 byte of RAM in your Device for storing the last DMX Value.


    You would only lose one of the 255 Values so you reduce the resolution and also make processing very complex.


    I think that by adding a null value overall the complexity in the uC would increase.

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