USB2504/USB2504A

DS000002250A-page 26

 2007 - 2016 Microchip Technology Inc.

5.3.9.18

Undefined Registers

The registers shown in Table 5-4 are the defined registers in the Hub. Reads to undefined registers return 00h. Writes

to undefined registers have no effect and do not return an error.

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 Microchip 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 15 for the internal default values that are loaded when this option is selected.

5.5

Default Strapping Options:

The Microchip Hub can be configured via a combination of internal default values and pin strap options. Please see

Table 4-1, "4-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 15 for

the internal default values that are loaded when this option is selected.

The Amber and 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 signaling, 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 signaling, and the PAD will “source” the current to the external

LED.

FIGURE 5-1:

LED STRAPPING OPTION

HUB

50K

Strap Low

GR2

50K

Strap High

GR1

+V