AN985B/BX
Functional Descriptions
MAC Control Frame and PAUSE Frame
Figure 13 MAC Control Frame Format
The MAC Control frame is distinguished from other MAC frames only by their Length/Type field identifier. The MAC
Control Opcode defined in MAC Control Frame format for PAUSE function is 0001H. Also, the PAUSE time is
specified in the MAC Control Parameters field with 2 Octets, unsigned integer, in the units of Slot-Times. The
range of possible PAUSE time is 0 to 65535 Slot-Times.
So, a valid PAUSE frame issued by a MAC control client (could be a switch or a bridge) which will contain:
1. The destination address set equal to the globally assigned 48 bit mulitcast address 01-80-C2-00-00-01, or
equal to the unicast address which the MAC control client wishes to inhibit its transmission of data frames
2. Filled MAC Control Opcode field with 0001H
3. 2 Octets of PAUSE time specified in the MAC Control parameter field to indicate the length of time for which
the destination is wished to inhibit data frame transmission
Receive Operation for PAUSE Function
Upon reception of a valid MAC Control frame, the AN985B/BX will start a timer for the length of time specified by
the MAC Control Parameters field. When the timer value reaches zero then the AN985B/BX ends PAUSE state.
However, a PAUSE frame should not affect the transmission of a frame that has been submitted to the MAC
(started Transmit out of the MAC and can’t be interrupted). On the other hand, the AN985B/BX shall not begin to
transmit a frame more than one Slot-Times after receiving a valid PAUSE frame with a non-zero PAUSE time. If
the AN985B/BX receives a PAUSE frame with a zero PAUSE time value, the AN985B/BX ends the PAUSE state
immediately.
Data Sheet
29
Rev. 1.51, 2005-11-30
INFINEON [ Infineon ]
