NS32491

The DP8391 Serial Network Interface (SNI) provides the Manchester data encoding and decoding functions for IEEE 802.3 Ethernet/Cheapernet type local area networks.

The SNI interfaces the DP8390 Network Interface Controller (NIC) to the Ethernet transceiver cable. When transmitting, the SNI converts non-return-to-zero (NRZ) data from the controller and clock pulses into Manchester encoding and sends the converted data differentially to the transceiver. The opposite process occurs on the receive path, where a digital phase-locked loop decodes 10 Mbit/s signals with as much as g20 ns of jitter.

The DP8391 SNI is a functionally complete Manchester encoder/ decoder including ECL like balanced driver and receivers, on board crystal oscillator, collision signal translator, and a diagnostic loopback circuit. The SNI is part of a three chip set that implements the complete IEEE compatible network node electronics as shown below. The other two chips are the DP8392 Coax Transceiver Interface (CTI) and the DP8390 Network Interface Controller (NIC).

Incorporated into the CTI are the transceiver, collision and jabber functions. The Media Access Protocol and the buffer management tasks are performed by the NIC. There is an isolation requirement on signal and power lines between the CTI and the SNI. This is usually accomplished by using a set of miniature pulse transformers that come in a 16-pin plastic DIP for signal lines. Power isolation, however, is done by using a DC to DC converter.