4-Port USB2.0 Controller

Datasheet

SMSC USB20H04

Page 21

Revision 1.63 (10-14-04)

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.