I am working on a project with the STM32F407 communicating to a 8051 micro with i2c. I can read from the slave(8051) with no problems but when I try to send more than 3 bytes to the slave I get an ARBLOST error. I2C2_SR1 = 0x0200, Any ideas on what it could be? I've poured over the forums but cant find anything specific for interrupt driven code. The SDA and SCL lines are clean looking on the scope.