I am trying to control an Analog Devices programming resistor AD5254 by a USB to I2C master device from MicroChip MCP2221. The problem I am facing is that each time MCP2221 is waiting for ACK from AD5254, the SCL clock de-assert which i think affect the AD5254 to not be configured properly. This is what happens : 1. Using MicroChip I2C/SMbus Terminal I am sending the following : enter image description here 2. observing SDA/SCL using a scope + I2C protocol analyzer I can see the address+data are ok but after each Ack SCL line drops : enter image description here 3. I know that the address+data is correct because I am using Analog Devices Evaluation board for reference, and when connecting their SDP-B controller board (UG-277) to the Evaluation (UG-236) the SDA/SCL signals are correct : enter image description here

Anyone know why SCL drops after each ACK ?

  • \$\begingroup\$ Do you have write protect enabled hence it only stores the volatile value. SCL probably drops after an ACK because it can. \$\endgroup\$
    – Andy aka
    Commented Jun 17, 2019 at 9:27
  • \$\begingroup\$ The data looks fine except something is stretching the clock \$\endgroup\$
    – pm101
    Commented Jun 17, 2019 at 10:47
  • \$\begingroup\$ thanks Andy, that was it ! you helped finish couple of days debug ! \$\endgroup\$ Commented Jun 17, 2019 at 11:48


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