On Mittwoch, 21. Februar 2007 gazoox22 wrote:
> Greetings.
>
> For now, I have tested your code. It runs, but what I get from the I2C
> bus is the byte 0x80, so I think the PCF8591 is sending something
> back. At the moment I dont' use any pull up resistors, but get the
> same results with 10k on SCK and/or SDA. My Vref is 3,3V.
>
> Please help.
I'm not quite sure what your problem is, but 0x80 as the first data to be
returned from an PCF8591 is correct.
The inner workings of the chip are (see also datasheet):
A read operation starts a new AD-conversion cycle, and returns the value from
the _last_ conversion.
Since there has been no conversion on a newly attached device, the first data
to be returned from a PCF8591 is always 0x80. The next read-operation will
return the result of the conversion triggered by the first read.
Eberhard
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