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PCF8575C Usage Question

Sean Rauchfuss
Intellectual 1005 points
Other Parts Discussed in Thread: PCF8575C, TCA9535, TCA9555

Posting for a customer:

What I need from TI regarding the PCF8575C is the following:

1.  byte/word command set AND required command sequence that the chip wants to see in order to set/clear bits which are set as outputs

2.  byte/word command set AND required command sequence that the chip wants to see in order to read bytes OR words

I've done the following:

1.  wrote python script which successfully scans the i2c bus for the two chips I've addressed as 000 and 001; the scan returns corresponding i2c addresses found at 0x20 and 0x21 - I'm pretty sure this is correct.

2.  tried writing to the devices at 0x20 & 0x21 using two and three separate byte-writes; one for device address, one for write register address (0x40), and one for the data which should set all bits high (0xFF)..nothing here works

Summarizing, I'm using an FT232H configured as an MPSSE device as the i2c bus master, and I can find the two pcf8575c devices i2c addresses with the FT232H, but I'm having trouble writing & reading bits 0..15.

  • 0
    TI__Genius 16450 points
    Hello,

    I have reached out to the appropriate apps engineer for the PCF product.
  • 0
    TI__Genius 16450 points
    Hello,

    Try having him write the slave address and 0xFF.

    There is no register address he must supply to the device, instead he writes the data to the ports directly.

    Have him read section 8.1 on page 11 of the datasheet.

    In another note, if he's driving more than few microamps of load, he should switch to a TCA9535 (or TCA9555, we can discuss the options) which DOES have registers (the way he's currently writing)