CY7C656xx
Document #: 38-08037 Rev. *J
Page 4 of 25
Downstream Ports
The CY7C656xx supports a maximum of four downstream ports,
each of which may be marked as usable or removable in the
extended configuration (0xD2 EEPROM load or 0xD4 EEPROM
load, see Configuration Options on page 12. Downstream D+
and D– pull down resistors are incorporated in CY7C656xx for
each port. Before the hubs are configured, the ports are driven
SE0 (Single Ended Zero, where both D+ and D– are driven low)
and are set to the unpowered state. Once the hub is configured,
the ports are not driven, and the host may power the ports by
sending a SetPortPower command for each port. After a port is
powered, any connect or disconnect event is detected by the
hub. Any change in the port state is reported by the hubs back
to the host through the Status Change Endpoint (endpoint 1).
Upon receipt of SetPortReset request for a port with a device
connected, the hub does as follows:
■ Performs a USB Reset on the corresponding port
■ Puts the port in an enabled state
■ Enables the green port indicator for that port (if not previously
overridden by the host)
■ Enables babble detection once the port is enabled.
Babble consists of a non-idle condition on the port after EOF2. If
babble is detected on an enabled port, that port is disabled. A
ClearPortEnable request from the host also disables the
specified port.
Downstream ports can be individually suspended by the host
with the SetPortSuspend request. If the hub is not suspended, a
remote wakeup event on that port is reflected to the host through
a port change indication in the Hub Status Change Endpoint. If
the hub is suspended, a remote wakeup event on this port is
forwarded to the host. The host may resume the port by sending
a ClearPortSuspend command.
Upstream Port
The upstream port includes the transmitter and the receiver state
machine. The transmitter and receiver operate in high speed and
full speed depending on the current hub configuration.
The transmitter state machine monitors the upstream facing port
while the Hub Repeater has connectivity in the upstream
direction. This machine prevents babble and disconnect events
on the downstream facing ports of this hub from propagating and
causing the hub to be disabled or disconnected by the hub to
which it is attached.
Power Switching
The CY7C656xx includes interface signals for external port
power switches. Both ganged and individual (per-port) configu-
rations are supported, with individual switching being the default.
Initially all ports are unpowered. After enumerating, the host may
power each port by sending a SetPortPower request for that port.
The power switching and over-current detection of downstream
ports is managed by control pins connected to an external power
switch device. PWR [n]# output pins of the CY7C656xx series
are connected to the respective external power switch's port
power enable signals. (Note that each port power output pin of
the external power switch must be bypassed with an electrolytic
or tantalum capacitor as required by the USB specification.
These capacitors supply the inrush currents, which occur during
downstream device hot-attach events.) The polarity of this pin
can be configured through the EEPROM; see 0xD4 Load on
page 13.
Overcurrent Detection
Overcurrent detection includes 8 ms of timed filtering by default.
This parameter is configured from the external EEPROM in a
range of 0 ms to 15 ms for both enabled ports and disabled ports
individually. Detection of over-current on downstream ports is
managed by control pins connected to an external power switch
device.
The OVR[n]# pins of the CY7C656xx series are connected to the
respective external power switch's port over-current indication
(output) signals. After detecting an over-current condition, hub
reports overcurrent condition to the host and disables the PWR#
output to the external power device. The polarity of the OVR pins
can be configured through the EEPROM; see 0xD4 Load on
page 13.
Port Indicators
The USB 2.0 port indicators are also supported directly by
CY7C656xx. According to the specification, each downstream
port of the hub optionally supports a status indicator. The
presence of indicators for downstream facing ports is specified
by bit 7 of the wHubCharacteristics field of the hub class
descriptor. The default CY7C656xx descriptor specifies that port
indicators are supported (wHubCharacteristics, bit 7 is set). If
port indicators are not included in the hub, disable this bit through
EEPROM settings.
Each port indicator pin is strategically located directly on the
opposite edge of the port with which it is associated. A port
indicator provides two colors: green and amber. This is usually
implemented as two separate LEDs, one amber and the other
green. A combination of hardware and software control is used
to inform the user of the current status of the port or the device
attached to the port and to guide the user through problem
resolution. Colors and blinking provide information to the user.
The significance of the color of the LED depends on the opera-
tional mode of CY7C656xx. The CY7C656xx port indicators has
two modes of operation: automatic and manual.
On power up the CY7C656xx defaults to automatic mode, where
the color of the Port Indicator (green, amber, off) indicates the
functional status of the CY7C656xx port. In automatic mode, the
CY7C656xx turns on the green LED whenever the port is
enabled and the amber LED when an overcurrent condition is
detected. The color of the port indicator is set by the port state
machine. Blinking of the LEDs is not supported in automatic
mode. Table 1 identifies the mapping of color to port state in
automatic mode.
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