AM79C983AKCW AMD [Advanced Micro Devices], AM79C983AKCW Datasheet - Page 48

• Manufacturer Part Number: AM79C983AKCW
• Manufacturer: AMD [Advanced Micro Devices]

Port Switching
Port switching allows the movement of individual ports
between multiple Ethernet collision domains via soft-
ware. This capability enables the network manager to
optimize network performance by dynamically balanc-
ing the loads on a network. As an example, a port ex-
hibiting a high level of activity can be moved to a less
congested collision domain.
The method of implementing port switching with the
IMR2/QuIET chip set is to connect a single transceiver
port to multiple IMR2 devices. The number of IMR2 de-
vices will equal the number of backplanes supported in
the hub. 11 is a simplified schematic showing a hub
with three separate backplanes. Only one QuIET de-
vice is shown for simplicity, although it is expected that
most applications will use three QuIET devices to en-
able 12 port multiples.
The following discussion of port switching will con-
sider only port 0; although, it is equally applicable to
all of the ports. At any time, PAUI 0 is enabled on one,
and only one, IMR2 device. As a result, port 0 is trans-
ferred to whichever IMR2 device has PAUI 0 enabled.
48
Am79C90 (C-LANCE)
RCLK
CLSN
RENA
TENA
TCL
RX
TX
Figure 10. PR Port Connection to an Am79C90 C-Lance
Generator
Clock
P R E L I M I N A R Y
Am79C983A
The other two IMR2 devices will have PAUI 0
disabled with PDO 0 in a high impedance state. To
move port 0 to another backplane, the software will
disable PAUI 0 on the active IMR2 device and enable
PAUI 0 on the targeted IMR2 device that represents
the desired backplane. Pseudo AUI ports can be
disabled or enabled by setting the appropriate bit in
the Port Switching Control Register.
Although there are multiple IMR2 devices, only one has
management control of the QuIET devices. 11 shows
IMR2 device 0 having management control. The other
two devices do not have any control over the configura-
tion of the QuIET devices.
The number of IMR2 devices that can be connected to-
gether is limited by the load on the PAUI drivers. The
PAUI will operate reliably with a load up to 100 pF. On
a system that uses sockets for the IMR2 devices, the
maximum number of devices is six. This number can in-
crease as long as the total load capacitance is kept
below 100 pF.
DAT
MACEN
ECLK
4.9 k
+5 V
PENAO
PENAI
COL
JAM
PDRV
PDAT
PCLK
19879B-14