Datasheet

Platform Cable USB
DS300 (v3.3) June 25, 2014 www.xilinx.com
Product Specification 16
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Hub Types and Cable Performance
There are two important hub specifications that affect the
performance of Platform Cable USB: maximum port current
and total bandwidth.
Maximum Port Current
Platform Cable USB is a bus-powered device that draws
less than 100 mA from the host USB port under all
operating conditions.
Note:
The DLC9G and legacy DLC9LP cable models draw less
than 100 mA from the host USB port. The legacy DLC9 cable
model requires 230 mA to operate in USB 2.0 Hi-Speed mode or
150 mA to operate in USB 2.0/1.1 full-speed mode. Some older
root hubs or external bus-powered hubs might restrict devices to
100 mA. The legacy DLC9 cable model does not enumerate on
hubs with the 100 mA restriction.
Total Bandwidth
The maximum achievable bandwidth for a single USB 1.1
full-speed device is 8 Mb/s. The maximum theoretical
bandwidth for a single USB 2.0 Hi-Speed device is 56 Mb/s.
Because hub bandwidth must be shared among all
connected devices, actual bandwidth could be lower.
If Platform Cable USB is attached to a 1.1 hub, configuration
speed is degraded. Communication overhead and protocol
limit any given device to approximately 30% of total
bandwidth. For 1.1 hubs, the best achievable throughput is
approximately 3.6 Mb/s (refer to Figure 29).
If an external 2.0 hub is attached to a 1.1 root hub, operation
is at full speed (refer to Figure 29B). Hi-Speed USB
operation is guaranteed only if Platform Cable USB is
attached directly to a 2.0 root hub, or to an external self-
powered 2.0 hub that is connected to a 2.0 root hub (refer to
Figure 29D and Figure 29E).
If Platform Cable USB is attached to an external, bus-
powered 2.0 hub, it could enumerate as a full-speed device
(refer to Figure 29C). Bus-powered hubs can deliver a total
of 500 mA to all connected devices. If individual ports on
bus-powered hubs are limited to less than 150 mA, Platform
Cable USB does not enumerate and is unavailable for use
by host software applications.
X-Ref Target - Figure 29
Figure 29: Platform Cable USB Performance with Various Hub Types
1.X Root Hub
Platform Cable
USB
12 Mb/s Bus Speed
1.X Root Hub
Platform Cable
USB
2.0 Root Hub
Platform Cable
USB
480 Mb/s Bus Speed
2.0 External
Bus-Powered
Hub
12 Mb/s Bus Speed
2.0 External
Bus-Powered
Hub
Platform Cable
USB
2.0 Root Hub
480 Mb/s Bus Speed
2.0 External
Self-Powered
Hub
500
mA
500
mA
< 500
mA
500
mA
500
mA
< 500
mA
2.0 Root Hub
Platform Cable
USB
500
mA
480 Mb/s Bus Speed
500
mA
(A) (B) (C) (D) (E)
Power
DS300_27_021607
Ty pically, enumerates
at full-speed because
bus-powered external
hub supplies < 500 mA
per port — Possible
degraded performance
due to slow bus speed
Enumerates at
full-speed because
root hub only
operates at full-speed
— Degraded
performance due to
slow bus speed
Enumerates at
Hi-Speed since external
self-powered hub can
supply 500 mA per port
— Best performance
due to high bus speed
Enumerates at
full-speed because
root hub only
operates at full
speed —
Degraded
performance due
to slow bus speed
Enumerates at
Hi-Speed since
root hub can
supply 500 mA
per port — Best
performance due
to high bus speed