Datasheet

2.0 Functional Description (Continued)

27 www.national.com

The Manchester encoder accepts NRZ data from the MII,

encodes the data to Manchester and sends it to the driver.

The driver transmits the data differentially to the trans-

ceiver.

2.6.2 AUI/TP Autoswitch

The DP83843 has an autoswitching feature that allows

switching between the AUI and TP operation. The AUI/TPI

autoswitch feature (AUTOSW_EN) is enabled by bit 9 of

the 10BASE-T Control and Status Register (10BTSCR). If

AUTOSW_EN is asserted (default is de-asserted) and the

DP83843 is in 10 Mb/s mode it automatically activates the

TPI interface (10 Mb/s data is transmitted and received at

the TPTD+/− and TPRD+/− pins respectively). If there is an

absence of link pulses, the transceiver will switch to AUI

mode. Similarly, when the transceiver starts detecting link

pulses it will switch to TP mode. The switching from one

mode to the next is only done after the current packet has

been transmitted or received. If the twisted pair output is

jabbering and gets into link fail state, then the switch to AUI

mode is only done after the jabbering is done, including the

time it takes to unjab (unjab time).

2.6.3 Ethernet Cable Configuration / THIN Output

The DP83843 offers the choice of Thick Ethernet

(10BASE5) and Thin Ethernet (10BASE-2). The type of

cabling used is controlled through bit 3 of the 10BTSCR

output signal which can be used to disable/enable an exter-

nal DC-DC converter which is required for 10BASE-2 appli-

cations to provide electrical isolation. This enables a

10BASE-2 and10BASE-5 common interface application.

Figure 1. AUI Typical Setup

15 Pin D AUI Connector

100uH

39Ω

.01uf

AUITD

AUIRD

AUICD

200Ω