ST802RT1AFR datasheet(43/58 Pages) STMICROELECTRONICS

43 / 58 page

ST802RT1A, ST802RT1B

Device operation

Doc ID 17049 Rev 1

43/58

7.12

Reset operation

There are two ways to reset the ST802RT1x.

Hardware reset: the ST802RT1x can be reset via the RESET pin (pin 29). The active low

reset input signal is required for at least 1 ms, and at least one transition is required on the

MDC (pin 31) to ensure proper reset operation.

Software reset: when bit 15 of register RN00 is set to 1, the ST802RT1x resets all the

circuits and registers to their default values, then clears bit 15 of RN00 to 0.

Both hardware and software reset operations initialize all registers to their default values.

This process includes re-evaluation of all hardware-configurable registers. Logic levels on

several I/O pins are detected during the hardware reset period to determine the initial

functionality of the ST802RT1x. Some of these pins are used as outputs after the reset

operation. Care must be taken to ensure that the configuration setup does not interfere with

normal operation. Strap pins multiplexed with LED outputs should be weakly pulled up or

weakly pulled down through resistors, as shown in Figure 6.

7.13

Preamble suppression

Preamble suppression mode in the ST802RT1x is indicated by a 1 in bit six of the RN01

in the system support preamble suppression, then a preamble is not necessary for each

management transaction. The first transaction following power-up/hardware reset requires

32 bits of preamble. The full 32-bit preamble is not required for each additional transaction.

The ST802RT1x responds to management accesses without preamble, but a minimum of

one idle bit between management transactions is required as specified in IEEE 802.3u.

7.14

Remote fault

The remote fault function indicates to a link partner that a fault condition has occurred by

using the remote fault bit, which is encoded in bit 13 of the link code word. A local device

indicates to its link partner that it has found a fault by setting the remote fault bit in the auto-

negotiation register to logic one and renegotiating with the link partner. The remote fault bit

remains at logic one until successful negotiation with the link code word occurs. The bit then

returns to 0. When the message is sent that the remote fault bit is set to logic one, the

device sets the remote fault bit in the MII to logic one if the management function is present.

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