am79c982 Advanced Micro Devices, am79c982 Datasheet - Page 14

• Manufacturer Part Number: am79c982
• Description: Basic Integrated Multiport Repeater Bimr
• Manufacturer: Advanced Micro Devices

Implementing a 12-Port Unmanaged Hub
Both bIMR4 and bIMR8 chips have an expansion bus
that allows multiple devices to be connected together,
allowing high port count repeaters to be designed. The
operation of the expansion bus is identical for the bIMR4
and bIMR8. Minimum Mode is available in both bIMR4
and bIMR8 devices. This mode facilitates the
implementation of the LED display for unmanaged hub.
Figure 2 shows a simple example where one four port
bIMR device and one eight port bIMR device are con-
nected together to form one twelve port logical
unmanaged repeater. As both devices are on the same
board the arbiter function can be local, and the bus
transceivers shown at right in Figure 1 are not
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Am79C982
necessary due to the low bus loading in this example. In
this case, the arbiter simply asserts ACK if one REQ sig-
nal is asserted and COL if both REQ signals are as-
serted. The arbiter does not assert either signal if neither
REQ is asserted. Note that both ACK and COL are logic
low when asserted.
The D type flip flop is used to synchronize the reset
signals to both bIMR devices in order to ensure that the
internal 10 MHz clocks of these devices are in phase.
More complex repeaters, including stackable hubs, may
be built using the bIMR family. In these cases, the bus
transceivers may be necessary and the arbitration may
be distributed throughout the system.