GL850A USB 2.0 Low-Power HUB Controller
5.1.10. TT (Transaction Translator)
TT implements the control logic defined in section 11.14 ~ 11.22 of USB specification Revision 2.0. TT
basically handles the unbalanced traffic speed between the USPORT (operating in HS) and DSPORTS
(operating in FS/LS) of hub. GL850A adopts the single TT architecture to provide the most cost effective
solution. Single TT shares the same buffer control module for each downstream port. GL852 adopts
multiple TT architecture to provide the most performance effective solution. Multiple TT provides control
logics for each downstream port respectively. Please refer to GL852 datasheet for more detailed
information.
5.1.11 REPEATER/TT routing logic
REPEATER and TT are the major traffic control machines in the USB 2.0 hub. Under situation that
USPORT and DSPORT are signaling in the same speed, REPEATER/TT routing logic switches the traffic
channel to the REPEATER. Under situation that USPORT is in the high speed signaling and DSPORT is in
the full/low speed signaling, REPEATER/TT routing logic switches the traffic channel to the TT.
5.1.11.1 Connected to 1.1 Host/Hub
If an USB 2.0 hub is connected to the downstream port of an USB 1.1 host/hub, it will operate in USB 1.1
mode. For an USB 1.1 hub, both upstream direction traffic and downstream direction traffic are passing
through REPEATER. That is, the REPEATER/TT routing logic will route the traffic channel to the
REPEATER.
USB1.1 HOST/HUB
USPORToperating
in FS signaling
Traffic channel
is routed to
TT
REPEATER
REPEATER
DSPORT operating
in FS/LS signaling
Figure 5.1 – Operating in USB 1.1 scheme
5.1.11.2 Connected to USB 2.0 Host/Hub
If an USB 2.0 hub is connected to an USB 2.0 host/hub, it will operate in USB 2.0 mode. The upstream port
signaling is in high speed with bandwidth of 480 Mbps under this environment. The traffic channel will
then be routed to the REPEATER when the device connected to the downstream port is signaling also in
high speed. On the other hand, the traffic channel will then be routed to TT when the device connected to
the downstream port is signaling in full/low speed.
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