AX88196BLF datasheet(27/86 Pages) ASIX

27 / 86 page

ASIX ELECTRONICS CORPORATION

AX88196BLF

4.4 Flow Control

The AX88196B supports Full-duplex flow control using the pause control frame. It also supports half-duplex flow

control using collision base of back-pressure method.

4.4.1 Full-Duplex Flow Control

The format of a PAUSE frame is illustrated below. It conforms to the standard Ethernet frame format but includes a

unique type field and other parameters as follows:

The destination address of the frame may be set to either the unique DA of the station to be paused, or to the globally

assigned multicast address 01-80-C2-00-00-01 (hex). The IEEE 802.3 standard for use in MAC control PAUSE

frames has reserved this multicast address. The "Type" field of the PAUSE frame is set to 88-08 (hex) to indicate the

frame is a MAC Control frame.

The MAC Control opcode field is set to 00-01 (hex) to indicate the type of MAC Control frame being used is a

PAUSE frame. The PAUSE frame is the only type of MAC Control frame currently defined.

The MAC Control Parameters field contains a 16-bit value that specifies the duration of the PAUSE event in units of

512-bit times. Valid values are 00-00 to FF-FF (hex). If an additional PAUSE frame arrives before the current

PAUSE time has expired, its parameter replaces the current PAUSE time, so a PAUSE frame with parameter zero

allows traffic to resume immediately.

A 42-byte reserved field (transmitted as all zeros) is required to pad the length of the PAUSE frame to the minimum

Ethernet frame size.

Preamble

(7-bytes)

Start Frame

Delimiter

(1-byte)

Dest. MAC

Address

(6-bytes)

= (01-80-C2-

00-00-01)

Source

MAC

Address

(6-bytes)

Length/Type

(2-bytes)

= 802.3 MAC

Control

(88-08)

MAC Control

Opcode

(2-bytes)

= PAUSE

(00-01)

MAC Control

Parameters

(2-bytes)

= (00-00 to

FF-FF)

Reserved

(42-bytes)

= all zeros

Frame

Check

Sequence

(4-bytes)

AX88196B will inhibit transmit frames for a specified period of time if a PAUSE frame received and CRC is

correct. If a PAUSE request is received while a transmit frame is in progress, then the pause will take effect after the

transmitting is completed.

AX88196B base on “Rx Page Start Register” (CR page0 Offset 01h) and “Rx Page Stop Register”(CR page0 Offset

02h) to calculate and got the total of free page count can be used for store received packets. (One page equal to 256

bytes) The total of free page count will decrease when packets received. A programmable of high water

free-page-count in “Flow Control Register” (Offset 1Ah) used to measure the water level of receive buffer.

AX88196B use XOFF / XON flow-control method to avoid missing packet if receive buffer almost full. A XON

transmitting when the total of free page count equal to or less then “high water free-page-count”. A XOFF

transmitting when the total of free page count equal to or greater then (“high water free-page-count” + 6 pages).

Fig - 6 TX / RX Flow control

PAUSE frame

HOST

Packet

STOP

AX88796B

TX Flow Control

RX Flow Control

The total of

free pages count

Programmable of free-page-count

Start to generate XON

frame packet

generate XOFF frame

packet

High water mark

Low water mark

Packets in RX buffer

6 pages

AX88196BLF Datasheet(PDF) 27 Page - ASIX Electronics Corporation

AX88196BLF Datasheet(HTML) 27 Page - ASIX Electronics Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

Datasheet Download

Link URL