Random number generating apparatus for an interface unit of a carrier sense with multiple access and collision detect (CSMA/CD) ethernet data network

A single-chip data network controller, comprising:

• a plurality of network interface units;
• and
• a clock unit for clocking the network interface units in synchronism with each other, in which:
• each interface unit is configured for interfacing in accordance with the Carrier Sense with Multiple Access and Collision Detect (CSMA/CD) protocol, and includes a transmit backoff unit for implementing a backoff algorithm in response to a network collision signal and a random number;
• each interface unit comprises a random number generating apparatus including:
• a dual mode random number generator;
• and
• a multiplexer for switching the random number generator between modes in accordance with an address of a data packet being processed by the interface unit;
• the random number generator comprises a linear feedback shift register;
• the shift register has a plurality of stages;
• the multiplexer has two signal inputs connected to outputs of two of said stages respectively, a switch input connected to receive said address and an output connected in circuit to an input of the shift register;
• the shift register has 25 stages;
• and
• said signal inputs of the multiplexer are connected to stages 18 and 22 of the shift register respectively.