AT43USB326_06 Datasheet, PDF (71/102 Pages) ATMEL Corporation – Multimedia USB Keyboard Controller with Embedded Hub

AT43USB326
Hub and Port Power
Management
Overcurrent Sensing
Port Power Switching
Set by hardware due to babble, physical disconnect or overcurrent except for Port 1 in which
case it is set by hardware at EOF2 due to hardware events. Cleared by firmware via Host
request ClearPortFeature(PORT_ENABLE).
• Bit 0 – PCSC: Port Connect Status Change
0 = No change has occurred on Current Connect Status
1 = Current Connect Status has changed
This bit is set by hardware at EOF2 after it detects a connect or disconnect at a port, except for
Port 1. Hardware sets this bit for Port 5 after a hub reset. Cleared by firmware via Host request
ClearPortFeature(PORT_CONNECTION).
The embedded hub in a keyboard will most likely be a bus-powered hub even though the hard-
ware of the AT43USB326 is designed to accommodate both types of hubs. Management of
the downstream port power is also defined by the firmware: per port or global overcurrent
sensing, individual or gang power switching. While the interface to the external power supply
monitoring and switching is achieved through the microcontroller’s GPIO pins, the USB hard-
ware of the AT43USB326 contains the circuitry to handle all the possible combinations port
power management tasks.
If programmed for global overcurrent protection, the AT43USB326 is capable of detecting an
overcurrent in its downstream port even while it is in the suspend state. This mode is enabled
through the Overcurrent Detect Register, UOVCER, which controls the PD0 pin used for over-
current input sensing.
1. Global Overcurrent Protection – In this mode, the Port Overcurrent Indicator and
Port Overcurrent Indicator Change should be set to 0's. For the AT43USB326 an exter-
nal solid state switch, such as the Micrel MIC2545-2, is required to switch power to the
external USB ports. The FLG# output of the switch should be connected to PD0. When
an overcurrent occurs, FLG# is asserted and the firmware should set the Hub Overcur-
rent Indicator and Hub Overcurrent Indicator Change and switch off power to the hub.
2. Individual Port Over-current Protection – The Hub Overcurrent Indicator and Hub
Overcurrent Indicator Change bits should be set to 0's. One MIC2026-2 is required for
the two USB ports. Each of the FLG# outputs of the MIC2026-2 should be connected
to an unused microcontroller port. An overcurrent is indicated by assertion of FLG#.
The firmware sets the corresponding port's Overcurrent Indicator and the Overcurrent
Indicator Change bits and switches off power to the port. At the next IN token from the
Host, the AT43USB326 reports the status change.
1. Gang Power Switching – One of the microcontroller I/O port pins must be pro-
grammed as an output to control the external switch, PWRN. Switch ON is requested
by the USB Host through the SetPortFeature(PORT_POWER) request. Switch OFF is
executed upon receipt of a ClearPortFeature(PORT_POWER) or upon detecting an
overcurrent condition. The firmware clears the Power Control Bit. Only if all of the
Power Control Bits of ports 2 and 3 are cleared should the firmware de-assert the
PWRN pin.
2. Individual Power Switching – One microcontroller I/O port pin must be assigned for
each USB port to control the external switch, PWRxN, where x = 2, 3. Each of the
Power Control Bits controls one PWRxN.
3. Multiple Ganged Overcurrent Protection – Overcurrent sensing is grouped physi-
cally into one or more gangs, but reported individually.
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3313D–USB–04/06