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2-Port USB 2.0 Hub Controller
Datasheet
Revision 2.3 (08-27-07) 32 SMSC USB2502
DATASHEET
5.3.9.19 Reserved Registers
Unless otherwise instructed, only a ‘0’ may be written to all reserved registers or bits.
5.4 Default Configuration Option:
The SMSC Hub can be configured via its internal default configuration. (please see for specific details
on how to enable default configuration.
Please refer to Table 5.1 on page 19 for the internal default values that are loaded when this option is
selected.
5.5 Default Strapping Options:
The SMSC Hub can be configured via a combination of internal default values and pin strap options.
Please see Table 4.1, "7-Port Hub Pin Descriptions" for specific details on how to enable the
default/pin-strap configuration option.
The strapping option pins only cover a limited sub-set of the configuration options. The internal default
values will be used for the bits & registers that are not controlled by a strapping option pin. Please
refer to Table 5.1 on page 19 for the internal default values that are loaded when this option is selected.
The Green LED pins are sampled after RESET_N negation, and the logic values are used to configure
the hub if the internal default configuration mode is selected. The implementation shown below (see
Figure 5.1) shows a recommended passive scheme. When a pin is configured with a “Strap High”
configuration, the LED functions with active low signalling, and the PAD will “sink” the current from the
external supply. When a pin is configured with a “Strap Low” configuration, the LED functions with
active high signalling, and the PAD will “source” the current to the external LED.
Figure 5.1 LED Strapping Option
5.6 Reset
There are two different resets that the Hub experiences. One is a hardware reset (via the RESET_N
pin) and the second is a USB Bus Reset.
HUB
50K
Strap Low
GR2
50K
Strap High
GR1
+V