RTL8305S Ver la hoja de datos (PDF) - Realtek Semiconductor

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RTL8305S

5-PORT 10/100 MBPS SINGLE CHIP SWITCH CONTROLLER

Realtek Semiconductor 

RTL8305S

6.2.5 Flow Control

The RTL8305S supports IEEE 802.3x full duplex flow control and half duplex back-pressure congestion control. Once

the full duplex flow control ability is enabled via ENFCTRL, the Nway ability with full duplex flow control will be

negotiated during the auto-negotiation process. When operating in half duplex mode, a proprietary back-pressure

algorithm is enabled via the ENBKPRS pin, which can prevent traditional hub devices from partition due to excessive

collisions. For MII port applications, the same functions will be applied to port4 depending on the state of P4FLCTRL#

and P4DUPSTA#. If port4 is not configured to MII port application, it acts as a UTP port and behaves according to the

configuration of the ENFCTRL and ENBKPRS pins.

6.2.6 Back-off Algorithm

The RTL8305S implements the truncated exponential back-off algorithm compliant to the 802.3 standard. The collision

counter will be reset after 16 consecutive collisions, which leads to a smaller back-off time.

6.2.7 Inter-Frame Gap

The Inter-Frame Gap is 9.6us for 10Mbps Ethernet and 960ns for 100Mbps Fast Ethernet.

6.2.8 Illegal Frame

Illegal frames such as CRC error packets, runt packets ( packet length less than 64 bytes) and oversize packets (packet length

greater than 1536 bytes) will be discarded.

6.2.9 Broadcast Storm Control

The RTL8305S processes broadcast storm control via the latched value of the EnBrdCtrl pin upon reset. Once enabled, the

incoming consecutive broadcast packets will be discarded after consecutive 64 broadcast packets are received during an 800ms

time window. Any non-broadcast packets can reset the time window and broadcast counter such that the scheme restarts.

6.3 Physical Layer Functional Overview

6.3.1 Auto-negotiation

The RTL8305S obtains the states of duplex, speed and flow control ability through the auto-negotiation mechanism, defined in

IEEE802.3u specifications, for each UTP port. During auto-negotiation, each port advertises its ability to its link partner and

compares ability with those received from its link partner. By default, the RTL8305S advertises full capabilities (100Full,

100Half, 10Full, 10Half) together with flow control ability.

Asserting NWAYHALF# sets the Nway ability of the RTL8305S to half duplex only (100Half, 10Half). Deasserting

ENFCTRL sets the Nway ability without the flow control function. ENBKPRS is a pin to enable the half duplex flow control

scheme, which is defined in auto-negotiation. The MII port obtains its duplex, speed, flow control and link states from pins as

described in section 5.5.

6.3.2 10Base-T Transmit Function

The output 10Base-T waveform is Manchester-encoded and driven into the network medium. The internal filter shapes the

driven signals to reduce EMI emission, eliminating the need for an external filter.

6.3.3 10Base-T Receive Function

The Manchester decoder converts the incoming serial stream to NRZ data when the squelch circuit detects that the signal level

has exceeded the configured squelch level.

6.3.4 Link Monitor

The 10Base-T link pulse detection circuit always monitors the RXIP/RXIN pins for the presence of valid link pulses.

Auto-polarity is implemented to correct the detected reverse polarity of RXIP/RXIN signal pairs.

2002/02/19

11

Rev. 1.2

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