I can't read the Cvs

Discussion in 'DCC & Electronics' started by RovDan, Oct 14, 2010.

  1. RovDan

    RovDan New Member


    I realized my own command station DCC which works fine. Now, I want to improve it with the possibility of reading the Cv values of a Mobile decoder. I just want to catch the basic acknowledgment (pulse I > 60 mA). I did 2 tests :

    • a WRITE BYTE like this : 0 (broadcast adress) 236 (WRITE BYTE) 28 (Cv29 -1) 50 (for example) 194 (XOR). This command works fine. I see the ACK pulse on my scope and the new CV is OK.
    • a VERIFY BYTE like this : 0 (broadcast adress) 228 (VERIFY BYTE) 28 (Cv29 -1) 50 (for example) 202 (XOR). With this command, I can't see the ACK pulse on my scope
    • a VERIFY BIT like this : 0 (broadcast adress) 232 (VERIFY BIT) 28 (Cv29 -1) 232 (to verify that bit 0 is high) 28 (XOR). With this command, I can't see the ACK pulse on my scope
    I can see the ACK pulse when writing, but never when reading. I don't understand. I tried it on different decoders (Lentz Silver, Digitrax). I use the :

    Configuration Variable Access Instruction - Long FormThe long form allows the direct manipulation of all CVs[]. This instruction is valid both when the Digital Decoder has its long address active and short address active. Digital Decoders shall not act on this instruction if sent to its consist address. The format of the instructions using Direct CV addressing is:
    The actual Configuration Variable desired is selected via the 10 bit address with the two bit address(AA) in the first data byte being the most significant bits of the address. The Configuration variable being addressed is the provided 10 bit address plus 1. For example, to address CV#1 the 10 bit address is "00 00000000".
    The defined values for Instruction type (CC) are:
    CC=00 Reserved for future use
    CC=01 Verify byte
    CC=11 Write byte
    CC=10 Bit manipulation
    Type = "01" VERIFY BYTE
    The contents of the Configuration Variable as indicated by the 10 bit address are compared with the data byte (DDDDDDDD). If the decoder successfully receives this packet and the values are identical, the Digital Decoder shall respond with an the contents of the CV as the Decoder Response Transmission, if enabled.

    Why my decoders don't want to ACK after a verify message? It would be very kind if you could tell me where I am wrong. Thank you very very much from France...

    Best regards,
    Daniel ROVERCH


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