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Reading TI-ADS1115 in Tachyon — Parallax Forums

Reading TI-ADS1115 in Tachyon

artkennedyartkennedy Posts: 174
in General Discussion

When I use this code to read a conversion from a TI-ADS1115 ADC the LSB is all zeros. Anything wrong here? Using Tachyon Neon with EXTEND5v4 on Prop 1.

$90 := @ADC \ ( --- ) define CONSTANT for adc 8-bit I2C address - this is the I2C address for the ADC board

ADC16@ ( reg -- dat16 ) \ read contents from a TI-1115 register
W \ combine bytes into a word
I2C> \ that's all for now
;

Comments

  • artkennedyartkennedy Posts: 174

    OK, I was trying to use markdown and screwed up the code block. Here is the code unformatted:

    $90 := @ADC \ ( --- ) define CONSTANT for adc 8-bit I2C address - this is the I2C address for the ADC board

    ADC16@ ( reg -- dat16 ) \ read contents from a TI-1115 register
    W \ combine bytes into a word
    I2C> \ that's all for now
    ;

  • artkennedyartkennedy Posts: 174

    Well it is still messed up. Trying again:

    $90 := @ADC \ ( --- ) define CONSTANT for adc 8-bit I2C address - this is the I2C address for the ADC board

    ADC16@ ( reg -- dat16 ) \ read contents from a TI-1115 register
    W \ combine bytes into a word
    I2C> \ that's all for now
    ;

  • artkennedyartkennedy Posts: 174

    That was without any attempt to formatting. It leaves out most of the code. Don't understand.

  • artkennedyartkennedy Posts: 174

    I'll try it this way:

    Could also use a reminder of how to post code in the forum.

  • artkennedyartkennedy Posts: 174

    Alright I took the markdown tutorial ( after I found it ) ...

  • Peter JakackiPeter Jakacki Posts: 10,193

    Normally the last data byte read is nak'd but the timing diagram shows an ack. However it has a note (3) which says "master can leave SDA high to terminate a two=byte read operation" which probably needs to be done anyway if you are stopping there, and the timing diagram should have shown that. However it also implies that you can leave the device selected and just read more data bytes for more samples, although i would probably test that out.

    Here's my simplified version that issues a nak on the last byte. Whether I use SWAP B>W or 8<< + in the right place doesn't make a whole lot of difference.

    --- Get the ADC reading (reg ptr is set on 0)
pub GETADC ( -- dat16 ) <I2C $91 I2C! ackI2C@ 8<< nakI2C@ +  I2C> ;
---                     slave read   msb & scale last lsb add stop

    The register pointer probably would be reset to 0 at power-up and so there is no need to select the data register each time. My suggestion would be if you are not writing to any other registers then don't worry about it. However if you do want to write to a register then make sure you reset the register pointer on exit.

    --- Leave the register pointer set to 0 for GETADC (probably redundant as the pointer would probably default to 0)
pub !ADC                <I2C $90 I2C! 0 I2C! I2C> ;

    BTW
    To format code just use the backtick (above the tilde near your esc key) or select code from the format icon to the right of the unordered list icon.
    To format Inline code manually just backtick mycode backtick and for multiline it is three backticks on a line before and three after
    backtick backtick backtick
    my code
    more code
    and more code
    backtick backtick backtick

    After the first three backticks you can also specify an optional language for syntax highlighting if it is supported (no spaces)
    backtick backtick backtick python
    my Python code
    more code
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    backtick backtick backtick

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