ICS1892 datasheet(50/148 Pages) ICST

50 / 148 page

ICS1892, Rev. D, 2/26/01

February 26, 2001

Chapter 7

Functional Blocks

ICS1892 Data Sheet

7.5.4

10Base-T Operation: Idle

The ICS1892 10Base-T Idle Function transmits link pulses in the absence of data (that is, when the

MAC/repeater is not requiring it to transmit any data). During this time the link is Idle, and the 10Base-T Idle

Function begins periodically transmitting link pulses at a rate of one pulse every 16 ms, as defined in the

ISO/IEC 8802-3 standard. In 10Base-T mode, the ICS1892 transmits link pulses whenever the

MAC/repeater does not have any data available for transmission. The ICS1892 continues transmitting link

pulses while receiving data. Because link pulses indicate an idle state for a link, this situation does not

generate a Collision Detect signal (COL).

7.5.5

10Base-T Operation: Link Monitor

When the ICS1892 is in 10Base-T mode, the Link Monitor Function observes the data received by the

10Base-T Twisted-Pair Receiver to determine the link status. The results of this continual monitoring are

stored in the Link Status bit. The Station Management entity (STA) can access the Link Status bit in either

the Status Register (bit 1.2) or the QuickPoll Detailed Status Register (bit 17.0). This Link Status bit is a

latching low (LL) bit. (For more information on latching high and latching low bits, see Section 8.1.4.1,

“Latching High Bits” and Section 8.1.4.2, “Latching Low Bits”.)

The STA can control the execution of the Smart Squelch Function using bit 18.0 (the Smart Squelch Inhibit

bit in the 10Base-T Operations Register). The Squelch Inhibit bit allows an STA to control the ICS1892

Squelch Detection in 10Base-T mode. When an STA sets this bit to logic:

• Zero, before the ICS1892 can establish a valid link, the ICS1892 must receive valid 10Base-T data.

• One, before the ICS1892 can establish a valid link, the ICS1892 must receive both valid 10Base-T data

followed by an IDL.

The criteria used by the Link Monitoring Function to declare a link either valid (that is, ‘established’ or ‘up’)

or invalid (that is, ‘failed’ or ‘down’) depends upon the present state of the link and the incoming data. When

the 10Base-T link is:

• Valid, the Link Monitor Function continues to report the link as valid as long as it detects either data or

Normal Link Pulses (NLPs) on its Twisted-Pair Receiver. If the 10Base-T Operations Register’s Smart

Squelch Inhibit bit (bit 18.0) is:

– Enabled, before the 10Base-T link can be valid, there must be an IDL at the end of a data packet.

– Disabled, before the 10Base-T link can be valid, all that is needed is a data packet.

• Invalid, the Link Monitor Function must detect one of three events before transitioning the link from the

invalid state to the valid state. If the ICS1892 receives any of the following it changes the status of the

link from invalid to valid:

– More than seven Normal Link Pulses (NLPs)

– Any data

– Any data followed by a valid IDL

The ICS1892 receives data when the Twisted-Pair Receiver phase-locked loop can acquire lock and

extract the receive clock from the incoming data stream for three bit times.

If the ICS1892 receives neither data nor NLPs (that is, the link shows either no activity or inconsistent

activity) for more than 81 to 83 ms, then the ICS1892 declares the link invalid and sets the LL Link Status

bit to logic zero. The LL Link Status bit remains latched in the cleared state until a reset occurs or until

the STA reads it while the link is valid.

Note:

When the link is invalid and the ICS1892 detects the presence of data, the ICS1892 does not transition

the link to the valid state until after the reception of the present packet is complete.

Enabling or disabling the Smart Squelch Function affects the Link Monitor function.

A transition from the invalid state to the valid state does not automatically update the LL Link Status bit.

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