USB2.0 USBHUB

What is the USB 2.0 hub controller?

A USB hub Controller expands number of ports available from USB host. It is located between USB host and function devices.
It is used as a port enhancement to extend distance between USB host and function devices for access convenience. And it also provides power protection from over- current cause to malfunctioning device. Multiple devices can be designed as a single front end with hub to limit additional cable connections to host.
The USB 2.0 hub controller contains a logic block called Transaction Translator (TT) used for efficient data communication between High-Speed host and Full/Low-Speed function device. This allows Full-Speed (12 Mbps: FS) and Low-Speed (1.5 Mbps: LS) function device to communicate with host (via hub) in their respective speeds, while the data rate between host and hub remains running at High-Speed (480 Mbps: HS).

(2006/06)

What is Transaction Translator? What is difference between Single- TT and Multi-TT?

The Transaction Translator (TT) is a temporally buffer to translate data transaction of target LS/FS device connected to downstream ports of hub to HS bus.
A "Single-TT" hub (also called "per hub") device has one TT in the controller, and a "Multi-TT" hub (also called "per port") device has one TT for each port in the controller.
"Multi-TT" hub enables 12 Mbps bandwidth for each downstream port theoretically.
In reality, many devices, such as PC-cam, USB speaker and storage device which may require higher bandwidth, can operate simultaneously under "Single-TT" hub, without performance trouble.

(2006/06)

Can USB 2.0 compliant hubs connect to USB 1.1 host controller?

Yes, USB 2.0 is backward compatible. USB 2.0 hub operates in Full-speed mode when connecting to a USB 1.1 host port (UHCI or OHCI).
Of course the USB 2.0 hub operates in Hi-Speed mode, when it is attached to a USB 2.0 host port (EHCI).

(2006/06)

What are outlines of USB 2.0 hub controllers of NEC Electronics?

uPD720110A, 720112 and uPD720114 provide 4 downstream ports. uPD720113 provides 7 downstream ports.
Their each downstream port can connect to different (LS/FS/HS) speed device.
uPD720110A supports Self-powered mode. The package is 100-pin LQFP (14x14 mm).
uPD720112 and uPD70114 are lower power consumption products. Therefore, they have not only Self-Powered mode but also Bus-Powered mode. The packages are 80-pin TQFP (12x12mm) and 48-pin TQFP (9x9mm), respectively. They are applicable to box hub and VGA monitor hub.
uPD720113 is applicable to port replicator or docking station with expansion to more than 4 ports. The package is 80-pin TQFP (12x12mm).

(2006/06)

What are features of USB 2.0 hub controllers of NEC Electronics?

uPD720110A is the first USB 2.0 hub Controller in the world. Microsoft Corporation developed Windows driver software based on this hub Controller.
Moreover, almost all peripheral/system manufacturers developed and tested their USB products using NEC Electronics' hub controller. It is recognized as a de-fact standard.
uPD720112 and uPD720113 are second generation hub controllers based on the uPD720110A architecture. These are reduced power consumption, and implemented in smaller packages. They have external serial ROM interface to customize string descriptors, user own vendor/product IDs and system configuration data.
uPD720114 is the third generation hub controller. It is considered global environment, more low power consumption and low BOM cost. It can overall board design in miniature. It has 2.5V voltage regulator for core logic and termination resistors to reduce external components. The system configuration can be customized by strapping pin options, causing to external Serial ROM unnecessary.

(2006/06)

How does the power of hub supplied and managed?

There are two types of hub about power supply; Self-powered and Bus- powered hubs.
Self-powered hub has its own power supply, and has capability of supplying current up to 500mA for each downstream port. Bus-powered hub is supplied power by upstream (VBUS). It does not need local power supply, but the capability of supplying current is up to 100mA. Thus, a bus-powered hub cannot be connected to a high-powered device which requires more than 100mA.

	Self-Powered HUB	Bus-Powered HUB
Number of ports	Non limitation	Max. 4 (when the power is less than 100mA)
Max. output current per downstream port	500mA	100mA
Power supply	Local	From upstream
Connectable devices	All USB devices	Low powered or Self-Powered devices
Applications	Box hub, PC monitor, docking station, port replicator, etc.	Box hub, keyboard, port replicator, etc.

There are two types of power management of hub; Gang and Individual. The Gang method controls power by group, taking advantage of reducing power control components. However, when an over-current condition occurs at a port, all other ports will be also powered-off in the gang, causing to the communication will be broken. In the Individual method, over-current at a port will not effective to other ports, because the power is controlled individually.

(2006/06)

What is difference between "removable device" and "non- removable device"?

Non-removable device is fixed USB connection to a downstream port of hub. It cannot be disconnected from the port. An example is a USB keyboard with hub function. A device connected to a downstream port, such as box hub, is called removable device which can be disconnected.
If a hub is connected to non-removable device, the hub shows host the attribute of the port as "bDeviceRemovable" in Hub Descriptor (for more detail, please refer to User's Manual(User Registration is here).

Non- removable device reduces components such as connector, over-current protection, and power switch, because the plug is not swapped and power supply is shared.

(2006/06)

Can the uPD720114 operate on clock input?

No, clock input to the uPD720114 is prohibited.
The internal power supply and clock supply are stopped when the uPD720114 is in the Suspend mode.
Clock input at this time would damage the internal oscillator.
Further, since the Suspend mode is controlled by the host, no measures can be taken on the hub controller side.
If considering clock input for a 4-port hub controller, the uPD720112 is recommended.

(2006/12)

Can the number of downstream ports of hub controller be configured?

Yes, it is configurable.
uPD720114 can be configured it 2 to 4 by PPB4 and PPB3 pins.
uPD720112 and uPD720113 can be configured it by setting bNbrPorts value in external serial ROM.
uPD720110A can be configured it by either NUMPORT pin (to 3 ports) or setting external serial PROM.
For details, please refer to each User's Manual(User Registration is here).

(2006/06)

Why does the accuracy of resistor on RREF need to be +/- 1%?

The reference voltage for internal analog logic is generated from the RREF and the AVSS(R) inputs. Because the accuracy of this voltage level is critical, ±1% accuracy is required to the resistor (9.1kΩfor uPD720110A, 2.43kΩfor uPD720112, 720113, 720114).
In addition, the board layout should be designed to prevent noise from RREF pin.
For more detail, please refer to USB 2.0 PCB Design Guide (User Registration is here).

(2006/06)

Is it necessary to isolate AVDD (analog power) and VDD (digital power)?

Yes, it is necessary to isolate AVDD and VDD. AVDD is power supply for analog logic. This isolation provides low noise power to AVDD.

(2006/06)

Is an external serial ROM always required?

Serial ROM is not required to uPD720110A, 720112 and 720113, when their default descriptor is used.
This is recommended for general box hub application, and cost sensitive designs. When an application requires variation in number of ports, vendor specific Product ID or Vendor ID, external serial ROM is necessary.
uPD720114 does not have external serial ROM interface. However, it can be configured number of ports and so on by pin processing.
For details, please refer to each User's Manual (User Registration is here).

(2006/06)

Can a serial ROM for hub controller be shared with other devices?

No, it is not possible. A serial ROM is used solely by the hub controller.

(2006/06)

Can the external serial ROM be programmed after assembly?

uPD720110A does not have function to program external serial ROM for configuration. It must be programmed before board assembly or programmed by other circuit on the board.
uPD720112 and uPD720113 have capability of programming external serial ROM through upstream port. The programming tool is available for both DOS and Windows.

(2006/06)

Can a poly-fuse device be used instead of power switches?

It depends on requirement of system design.
Power switches are required for Bus-powered hub.
Self-powered hub must report status to system when over-current occurs. The over-current can be detected by either power switches or poly-fuses.

	Self-Powered HUB	Bus-Powered HUB
Power switches	Option	Required
Over-current protection	Required	Option

Note. Typical power switch has over-current detecting function.

(2006/06)

Is there any notification for board layout?

Please refer to USB 2.0 PCB Design Guide (User Registration is here).
Analog circuit and USB differential signals should be routed carefully to prevent noise.

(2006/06)

How to use LPWRM pin of uPD720112 and uPD720113?

uPD720112 and uPD720113 can monitor local power with LPWRM pin.
This pin is usually cramped to high by box hub or hub in a monitor. This allows hub to notify host PC when the local power is removed (e.g. AC adaptor is unplugged).
This is useful for docking station of mobile PC where battery is used. When LPWRM pin detects transition of the voltage level from "high" to "low", a hub changes all port states to "power-off", and reports it to the host. For more detail, please refer to each User's Manual(User Registration is here).
This pin will be set to high in typical design of a VGA monitor or normal box hub.

(2006/06)

How should unused pins be processed?

They should be processed as follows.

	uPD720112	uPD720113
DPx/DMx:	Low level
CSBx:	High level
PPBx:	Open
LPWRM:	High level
SCL:	Open
LEDx:	Open	NA (no pin)
AMBER	Open
GREEN	Open

(2006/06)