LAN9312 datasheet(58/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

Revision 1.2 (04-08-08)

SMSC LAN9312

DATASHEET

6.2.3

Flow Control Enable Logic

Each switch fabric port (0,1,2) is provided with two flow control enable inputs per port, one for

transmission and one for reception. Flow control on transmission allows the transmitter to generate

back pressure in half-duplex mode, and pause packets in full-duplex. Flow control in reception enables

the reception of pause packets to pause transmissions.

The state of these enables is based on the state of the ports duplex and Auto-negotiation settings and

the values of the corresponding Manual Flow Control register (Port 1 Manual Flow Control Register

(MANUAL_FC_1), Port 2 Manual Flow Control Register (MANUAL_FC_2), or Port 0(Host MAC)

Manual Flow Control Register (MANUAL_FC_MII)). Table 6.1 details the switch fabric flow control

enable logic.

When in half-duplex mode, the transmit flow control (back pressure) enable is determined directly by

the BP_EN_x bit of the ports manual flow control register. When Auto-negotiation is disabled, or the

MANUAL_FC_x bit of the ports manual flow control register is set, the switch port flow control enables

during full-duplex are determined by the TX_FC_x and RX_FC_x bits of the ports manual flow control

Figure 6.2 Switch Fabric CSR Read Access Flow Diagram

Idle

Write

Command

Read

Command

Read Data

CSR_BUSY = 0

CSR Read

CSR_BUSY = 1

Idle

Write

Command

Read

Command

CSR_BUSY = 0

CSR Read Auto

Increment /

Decrement

CSR_BUSY = 1

Write

Command

Read Data

last

data?

Yes

Read Data

min wait period

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