USB 2.0 Hi-Speed 2-Port Hub Controller
Datasheet
When HUB_RESUME_INHIBIT = ‘0’, Normal Resume Behavior per the USB 2.0 specification
When HUB_RESUME_INHIBIT = ‘1’, Modified Resume Behavior is enabled
Refer to the following subsections for additional details.
8.5.1
Normal Resume Behavior
VBUS_DET is used to detect presence of the Host. If VBUS_DET = ‘1’, then D+ pull-up is asserted
and normal USB functionality is enabled. The SUSP_IND provides an indication of the active or
suspended state of the hub.
The Hub will drive a ‘K’ on the upstream port if required to do so by USB protocol.
If VBUS_DET = ‘0’, then the D+ pull-up is negated. If battery charging is not enabled, the internal hub
logic will be reset, thus negating all downstream ports and associated downstream VBUS enable
signals. The hub will need to be re-enumerated to function, much like a new connect or after a
complete system reset.
8.5.2
Modified Resume Behavior
When the modified resume feature is enabled, the hub functions as follows:
VBUS_DET is used to detect presence of the Host. If VBUS_DET = ‘1’, then D+ pull-up is asserted
and normal USB functionality is enabled. SUSP_IND provides an indication of the active or suspended
state of the hub.
The device will drive a ‘K’ on the upstream port and downstream ports if required to do so by USB
protocol. The device will act as a controlling hub if required to do so by the USB protocol.
If VBUS_DET = ‘0’, then the D+ pull-up is negated, but the hub will not be internally reset. It will power-
on the downstream ports. The hub is able to continue to detect downstream remote wake events.
SUSP_IND provides an indication of the active or suspended state of the hub.
If a USB 2.0 specification compliant resume or wake event is detected by the device, the device is
remote wake enabled, and a port status change event occurs, SUSP_IND will be driven for the time
given in the GLOBAL_RESUME_TIME register.
If a remote wake event is detected on a downstream port:
1. Device disconnect
2. Device connect
3. A currently connected device requests remote wake-up.
Note: Downstream resume events are filtered for approximately 100uS by internal logic.
The device will not drive a ‘K’ on the upstream port. Instead, the SUSP_IND will be driven for
approximately 14 ms. The ‘K’ is not driven upstream because this would potentially back drive a
powered-down host. The device will drive RESUME to only the downstream ports which transmitted
the remote wake signal per the requirements of the USB 2.0 specification for controlling hub behavior.
Note: SUSP_IND is a one shot event. It will assert with each wake event detection. It will not
repeatedly assert in proxy for downstream devices.
For the case where the Host responds and turns on VBUS and can drive a ‘K’ downstream within the
14 ms time frame of a standard resume (measured from the SUSP_IND pin), then the hub detects the
‘K’. It will discontinue “Controlling Hub” activities, drive resume signaling on any other ports, and
SMSC USB2532
49
Revision 1.0 (06-17-13)
DATASHEET
SMSC [ SMSC CORPORATION ]
