29.2.4.1.2 WCOL Status Flag

If the user writes the SSPxBUF when a Start, Restart, Stop, Receive or Transmit sequence is in progress, the Write Collision Detect (WCOL) bit is set and the contents of the buffer are unchanged (the write does not occur). Any time the WCOL bit is set it indicates that an action on SSPxBUF was attempted while the module was not Idle.

Important: Because queuing of events is not allowed, writing to the lower five bits of SSPxCON2 is disabled until the Start condition is complete.