STE100A datasheet(25/82 Pages) STMICROELECTRONICS

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STE10/100A

Functional description

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3.5.3

Flow control in full duplex application

The PAUSE function is used to inhibit transmission of data frames for a specified period of

time. The STE10/100A supports the full duplex protocol of IEEE802.3x. To support the

PAUSE function, the STE10/100A implements the MAC Control Sub-layer functions to

decode the MAC Control frames received from MAC control clients and to execute the

relative requests accordingly. When full duplex mode and the PAUSE function are selected

after Auto-Negotiation completes (refer to the configuration of XR8), the STE10/100A will

enable the PAUSE function for flow control in a full duplex application. In this section we will

describe how the STE10/100A implements the PAUSE function.

MAC control frame and PAUSE frame

Figure 14.

MAC control frame format

The MAC control frame is distinguished from other MAC frames only by its length/type field

identifier. The MAC control opcode defined in MAC control frame format for the PAUSE

function is 0001h, and the PAUSE time is specified in the MAC control parameters field with

2 octets, representing an unsigned integer, in units of slot-times. The range of possible

PAUSE times is 0 to 65535 slot-times.

A valid PAUSE frame issued by a MAC control client (for example, a switch or a bridge)

would contain:

–

The destination address, set to the globally assigned 48 bit mulitcast address 01-

80-C2-00-00-01, or to the unicast address to which the MAC control client

requests to inhibit its transmission of data frames.

–

The MAC control opcode field set to 0001h.

–

2 octets of PAUSE time specified in the MAC control parameter field to indicate the

length of time for which the destination is requested to inhibit data frame

transmission.

Reserved (pads with zeroes)

MAC control parameter

MAC control Opcode

Lenght/Type = 88-08h

Source address

Destination address

Reserved (pads with zeroes)

MAC control parameter

MAC control Opcode

Lenght/Type = 88-08h

Source address

Destination address

(min frame size – 160) / 8 octets

2 octets

6 octets

(min frame size – 160) / 8 octets

2 octets

6 octets

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