LAN89218 datasheet(94/148 Pages) MICROCHIP

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LAN89218

DS60001255B-page 94

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5.3.22

AFC_CFG – AUTOMATIC FLOW CONTROL CONFIGURATION REGISTER

This register configures the mechanism that controls both the automatic, and software-initiated transmission of pause

frames and back pressure.

Offset:

ACh

Size:

32 bits

Note:

The LAN89218 will not transmit pause frames or assert back pressure if the transmitter is disabled.

Bits

Description

Type

Default

31:24

Reserved

23:16

Automatic Flow Control High Level (AFC_HI). Specifies, in multiples of 64

bytes, the level at which flow control will trigger. When this limit is reached the

chip will apply back pressure or will transmit a pause frame as programmed in

bits [3:0] of this register.

During full-duplex operation only a single pause frame is transmitted when

this level is reached. The pause time transmitted in this frame is programmed

in the FCPT field of the FLOW register in the MAC CSR space.

During half-duplex operation each incoming frame that matches the criteria in

bits [3:0] of this register will be jammed for the period set in the BACK_DUR

field.

R/W

00h

15:8

Automatic Flow Control Low Level (AFC_LO). Specifies, in multiples of 64

bytes, the level at which a pause frame is transmitted with a pause time set-

ting of zero. When the amount of data in the RX data FIFO falls below this

level the pause frame is transmitted. A pause time value of zero instructs the

other transmitting device to immediately resume transmission. The zero time

pause frame will only be transmitted if the RX data FIFO had reached the

AFC_HI level and a pause frame was sent. A zero pause time frame is sent

whenever automatic flow control in enabled in bits [3:0] of this register.

Note:

When automatic flow control is enabled the AFC_LO setting must

always be less than the AFC_HI setting.

R/W

00h

7:4

Backpressure Duration (BACK_DUR). When the LAN89218 automatically

asserts back pressure, it will be asserted for this period of time. This field has

no function and is not used in full-duplex mode. Refer to Table 5-5, describing

Backpressure Duration bit mapping, for more information.

R/W

Flow Control on Multicast Frame (FCMULT). When this bit is set, the

LAN89218 will assert back pressure when the AFC level is reached and a

multicast frame is received. This field has no function in full-duplex mode.

R/W

Flow Control on Broadcast Frame (FCBRD). When this bit is set, the

LAN89218 will assert back pressure when the AFC level is reached and a

broadcast frame is received. This field has no function in full-duplex mode.

R/W

Flow Control on Address Decode (FCADD). When this bit is set, the

LAN89218 will assert back pressure when the AFC level is reached and a

frame addressed to the LAN89218 is received. This field has no function in

full-duplex mode.

R/W

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