STE10A Datasheet, PDF (25/82 Pages) STMicroelectronics – PCI 10/100 Ethernet controller with integrated PHY (3.3V)

STE10/100A
Functional description
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
6 octets Destination address
6 octets _{Source address}
2 octets Lenght/Type = 88-08h
2 octets ^{MAC control Opcode}
MAC control parameter
Reserved (pads with zeroes)
(min frame size – 160) / 8 octets
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.
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