ADT7470 two byte I2C write supported?

ADT7470 datasheet rev. E says on page 10 that "In the ADT7470, write operations contain either one or two bytes".  When I try to do an I2C write with two bytes of data to the tach limit registers, I am seeing a NAK after the 2nd byte of write data.  Other places in the datasheet it only lists byte writes (Write Operations, p11-12).  Is two byte access supported?  If not what conditions would cause a nak on a write?

An example i2c write I see looks like this (adt7470 in bold):

<start><0x2c address><0 write><ack><0x62><ack><0xC1><ack><0x01><nak><stop>

  • Hi, 

    Can you share your schematics and the scope shot of the I2C lines above?



  • Schematic looks like this:

    The i2c lines also go to a Xilinx FPGA(master), pullups, AD7414 temp sensor and an LTC3350 supercap controller.

    The scope shot shows a write to I2C address 0x2c, subaddress 0x58 of 0xff, 0x07.  The tek0004 shot is the start of the transaction, tek0005 is the end (zoomed in a notch more).  SCL in yellow, SDA in blue.

  • Hi, Andrew.

    Apologies for the delayed response.TEK0005 looks like it got a stop condition. The datasheet states that “After all data bytes are read or written, stop conditions are established. In write mode, the master pulls the data line high during the 10th clock pulse to assert a stop condition.” I’d like to see TEK0004 in the zoomed in version like TEK0005 where I can distinguish the pulses. Did you mean to write 0x07 to register 0x58? 2-byte write is supported, as shown in Figure 7 of the datasheet. But note that "The first byte of a write operation always contains an address that is stored in the address pointer register. If data is to be written to the device, the write operation contains a second data byte that is written to the register selected by the address pointer register."



  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin