The first slot what is control cable (simply click the next document) reserved for a "Start Code" that specifies the type of data in the packet. A slot's position within the packet determines the device and function to be controlled while its data value specifies the control set point. Framed data bytes are known as slots. The break, which signals the end of one packet and the start of another, causes receivers to start reception and also serves as a frame (position reference) for data bytes within the packet. At the data link layer, a DMX512 controller transmits asynchronous serial data at 250 kbit/s. Fixed installation products with internal connections to the data link may use the 5-pin XLR connector, but shall not use any other XLR connector. Earlier versions of this standard assumed that only dimmer class data would be sent using NULL START Code packets. In practice NULL START Code packets have been used by a wide variety of devices; this version recognizes this fact.