Thank you for your reply, I will try your suggestions this weekend. The sensor can operate at 3.3V, I made sure to check for that specifically. I did not mean to make it sound like a simulation problem, I only posted the simulation to show that the master was meeting SDA/SCL time requirements. Everything mentioned in my post involves actual testing. I have a slave that I can write to and read from, I confirm this by writing the 8 bits to 8 LEDS, and I get ack and no ack depending if I send the correct address or not. So I know my master works in this sense at least. At the moment, I can't get an Ack, '0', back from the RGB slave when I first send the slave address, I am only getting no acks , '1'. I am assuming this is because I am not using the correct pull-up resistor and the RGB slave can't pull it down to a logic 0 for the FPGA to read. Hopefully what you said will fix that! Thank you again for your time!!