LXT970ATC datasheet(23/74 Pages) INTEL

23 / 74 page

Dual-Speed Fast Ethernet Transceiver — LXT970A

Datasheet

Test Loopback

A test loopback function is provided for diagnostic testing of the LXT970A. During test loopback

the twisted-pair interface is disabled. Data transmitted by the MAC is internally looped back by

the LXT970A and returned to the MAC.

Test loopback is available for 100 Mbps and 10 Mbps operation. Loopback paths for the two modes

of operation are shown in Figure 6.

Test loopback is enabled by setting bit 0.14 = 1 (loopback), bit 0.8 = 1 (full-duplex), and bit 0.12 =

0 (disable auto-negotiation). The desired mode of operation for test loopback is set using bits 0.13

and 19.2 as shown in Table 10.

Collision

The LXT970A asserts its collision signal, asynchronously to any clock, whenever the line state is

half-duplex and the transmitter and receiver are active at the same time. Table 11 summarizes the

conditions for assertion of carrier sense, collision, and data loopback signals.

Table 10. Test Loopback Operation

Mode of Operation

Bit

19.2

0.13

10 Mbps Test Loopback

100 Mbps Test Loopback

1. Also set bit 0.14 = 1, bit 0.8 = 1, and 0.12 = 0 to enable Test

Loopback.

Figure 6. Loopback Paths

Digital

Block

MII

Analog

Block

Driver

100 Mbps

Loopback

10 Mbps

Loopback

Table 11. Carrier Sense, Loopback, and Collision Conditions

Speed & Duplex Condition

Carrier Sense

Operational

Loopback

Collision

Full-Duplex at 10 Mbps or 100 Mbps

Repeater Mode

Receive only

None

100 Mbps, Half-Duplex

Transmit or Receive

None

Transmit and Receive

10 Mbps, Half-Duplex, 19.11 = 0

Transmit or Receive

Yes

Transmit and Receive

10 Mbps, Half-Duplex, 19.11 = 1

Receive only

None

Transmit and Receive

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