I2C code to write the DAC MCP4725


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  1. #1
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    Default I2C code to write the DAC MCP4725

    I am trying to control the DAC MCP4725 but my code seems not work . My code:

    sda var portb.4
    scl var portb.5

    cont var byte
    cont = %1100
    addr var byte
    addr = $60


    '=========================================
    writedac4725:

    I2CWRITE sda,scl,cont,addr,[4095] '12 bit value
    PAUSE 10 ' Wait 10ms for write to complete

    return
    '=========================================​


    The address of my board was confirmed $60 by reading the board with I2CScanner Arduino sketch
    The device control %1100 was from datasheet :


    https://ww1.microchip.com/downloads/...doc/22039d.pdf


    I would appreciate any help

    Thanks
    ACJacques

  2. #2
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    Default Re: I2C code to write the DAC MCP4725

    The address depends on the A2, A1 that are hardcoded into the chip at manufacturing time and also on the A0 that the user controls.

    I guess you have double checked them.

    Also the control byte I think should be a constant and not a variable.

    Ioannis

  3. #3
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    Default Re: I2C code to write the DAC MCP4725

    Richard from Support Melabs give me the solution:

    addr var byte
    addr = $C0 ;$60 <<1

    '==========================================
    writedac4725:
    I2CWRITE sda,scl,addr,[4000] '12 bit value
    PAUSE 10 ' Wait 10ms for write to complete
    return
    '=========================================

  4. #4
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    Default Re: I2C code to write the DAC MCP4725

    Richard from Support Melabs give me the solution:
    I should point out that I'm just an enthusiastic user on that forum and this one . I do not represent Melabs in any way shape or form
    Warning I'm not a teacher

  5. #5
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    Default Re: I2C code to write the DAC MCP4725

    Quote Originally Posted by acjacques View Post
    I2CWRITE sda,scl,addr,[4000] '12 bit value
    And that does work now?

    Ioannis

  6. #6
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    Default Re: I2C code to write the DAC MCP4725

    Code:
    addr var byte
    addr = $C0 ;$60 <<1
    
    writedac4725:
    I2CWRITE sda,scl,addr,[4000] '12 bit value
    PAUSE 10 ' Wait 10ms for write to complete
    That'll do a fast-mode write to the DAC register as long as the "12-bit value" is <4095, so you could remove the 'PAUSE 10'.
    If the upper control bits are '01x' then it'll possibly write to the DAC + EEPROM, depending on the actual value.

  7. #7
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    Default Re: I2C code to write the DAC MCP4725

    Isn't necessary the control byte?

    Ioannis

  8. #8
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    Default Re: I2C code to write the DAC MCP4725

    In fast mode (with the upper two bits 00) you only need two bytes.
    If you want to use the EEPROM function you need all three bytes.

    Of course, both modes need the address byte too.
    Last edited by tumbleweed; - 13th November 2023 at 17:44.

  9. #9
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    Default Re: I2C code to write the DAC MCP4725

    Yes. It is working in the Fast Mode.

    valuedac= 4095

    I2CWRITE sda,scl,%11000010,[valuedac.highbyte,valuedac.lowbyte]


    The above control byte in binary is from data sheet 1100 = device code
    0010 is the board with address code set to A0 = 1 . Most default boards are factory 0000. I have tied the user A0 bit to VCC in the board.
    Control and Address are in the same first byte.

    Data sheet says that second and third bytes may be repeated (valuedac may be repeated ) like
    I2CWRITE sda,scl,%11000010,[valuedac.highbyte,valuedac.lowbyte,valuedac.highby te,valuedac.lowbyte]
    This also works but seems be not necessary.

    I will try next days to write a code for other modes.

    Data Sheet link: https://ww1.microchip.com/downloads/...doc/22039d.pdf
    Last edited by acjacques; - 14th November 2023 at 02:22.

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