SMSC USB20H04 - Manual (Page 18)

4-Port USB 2.0 Hub Controller
Datasheet
Revision 1.63 (03-30-07) Page 18 SMSC USB20H04
DATASHEET
7.9 Transaction Translator (TT)
The transaction translator supports full-speed and low-speed devices attached to downstream ports in the
high-speed environment. To provide the highest level of performance, the USB20H04 Hub provides one
Transaction Translator (TT) per port (defined as multiple-TT).
7.10 Port Controller
The port controller provides status and control of individual downstream ports. Any port status change is
reported to the host via the hub status change (interrupt) endpoint.
7.11 Downstream PHY
Each of the downstream PHYs include a transmitter and receiver that operate in high-speed, full-speed or
low-speed mode, depending on the attached device. The required termination resistors are internal to the
USB20H04.
7.12 OC Sense/Switch Driver
One output per port is provided to control an external port power switch and one input per port is provided
to sense an external over-current sense. Both ganged and individual (per-port) configurations are
supported. See Figure 10.1 - High Level Block Diagram of a Self-Powered Hub for a typical
implementation.
7.12.1 Over-Current Sense
An external device monitors the current being provided to attached peripherals, and generates an output
during over-current conditions. This output is connected to the OCSx_N input of the USB20H04. This input
pin has an internal pull up resistor.
This input is filtered by the USB20H04 for the amount of time configured in the Over-Current Timer field
(See Table 8.4 - Address 8; Config_Byte_1) If the input continues to be asserted beyond the configured
time, the USB20H04 reports the over-current condition to the host and disables the power switch output
associated with that particular port. For use with typical silicon-based power controllers, configure the timer
to a value greater than zero to avoid glitches when devices are attached.
7.12.2 Switch Driver
Power to downstream ports is controlled by the VBUSx_N (where x stands for the port number) output
connected to an external power switch device. This output may be disabled when an over-current
condition has been reported, as described in Section 7.12.1.
7.13 LED Drivers
As per the specification, each downstream port of the hub supports an optional status indicator. The
USB20H04 provides one output per port for a green LED and one output per port for an amber LED.