VT6103

The VT6103 is a complete 10 / 100 Mbps Ethernet Media Interface IC. The VT6103 has the following main sections: controller interface, encoder, decoder, scrambler, descrambler, clock and data recovery, twisted pair transmitter, twisted pair receiver, and MI serial port. A block diagram is shown in Figure 3.

The VT6103 can operate as a 100Base-TX device (hereafter referred to as 100 Mbps mode) or as a 10Base-T device (hereafter referred to as 10 Mbps mode). The differences between 100 Mbps mode and 10 Mbps mode are data rate, signalling protocol, and allowed wiring. 100 Mbps TX mode uses two pairs of category 5 or better UTP or STP twisted pair cable with 4B5B encoded, scrambled, and MLT-3 coded 62.5 MHz ternary data to achieve a throughput of 100 Mbps. 10 Mbps mode uses two pairs of category 3 or better UTP or STP twisted pair cable with Manchester encoded, 10 MHz binary data to achieve a 10 Mbps thruput. The data symbol format on the twisted pair cable for the 100 and 10 Mbps modes is defined in the IEEE 802.3 specification.

On the transmit side for 100 Mbps TX operation, data is received on the controller interface from an external Ethernet controller. The data is then sent to the 4B5B encoder for formatting. The encoded data is then sent to the scrambler. The scrambled and encoded data is then sent to the TP transmitter. The TP transmitter converts the encoded and scrambled data into MLT-3 ternary format, preshapes the output, and drives the twisted pair cable.

On the receive side for 100 Mbps TX operation, the twisted pair receiver receives incoming encoded and scrambled MLT- 3 data from the twisted pair cable, removes any high frequency noise, equalizes the input signal to compensate for the effects of the cable, qualifies the data with a squelch algorithm, and converts the data from MLT-3 coded twisted pair levels to internal digital levels. The output of the twisted pair receiver then goes to a clock and data recovery block which recovers a clock from the incoming data, uses the clock to latch in valid data into the device, and converts the data back to NRZ format. The NRZ data is then unscrambled and decoded by the 4B5B decoder and descrambler, respectively, and outputted to an external Ethernet controller by the
controller interface. 10 Mbps operation is similar to 100 Mbps TX operation except (1) there is no scrambler/descrambler, (2) the encoder/decoder is Manchester instead of 4B5B, (3) the data rate is 10 Mbps instead of 100 Mbps, and (4) the twisted pair symbol data is two level Manchester instead of ternary MLT-3.

The Management Interface, (hereafter referred to as the MI serial port), is a two-pin bidirectional link through which configuration inputs can be set and status outputs can be read. Each block plus the operating modes is described in more detail in the following sections. Since the VT6103 can operate as either a 100Base-TX or a 10Base-T device, each of the following sections describes the performance of the respective section in both 100 and 10 Mbps modes.