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DS000002250A-page 19

USB2504/USB2504A

5.2.3.11

EEPROM Offset D(h) - Hub Controller Max Current For Self Powered Operation

5.2.3.12

EEPROM Offset E(h) - Hub Controller Max Current For Bus Powered Operation

5.2.3.13

EEPROM Offset F(h) - Power-On Time

5.3

SMBus Slave Interface

Instead of loading User-Defined Descriptor data from an external EEPROM, the Microchip Hub can be configured to

receive a code load from an external processor via an SMBus interface. The SMBus interface shares the same pins as

the EEPROM interface, if CFG_SEL1 & CFG_SEL0 activates the SMBus interface, external EEPROM support is no

longer available (and the user-defined descriptor data must be downloaded via the SMBus). Due to system issues, the

Microchip Hub waits indefinitely for the SMBus code load to complete and only “appears” as a newly connected device

on USB after the code load is complete.

The Hub’s SMBus implementation is a subset of the SMBus interface to the host. The device is a slave-only SMBus

device. The implementation in the device is a subset of SMBus since it only supports two protocols.

The Write Byte and Read Byte protocols are the only valid SMBus protocols for the Hub. The Hub responds to other

protocols as described in Section 5.3.2, "Invalid Protocol Response Behavior," on page 20. Reference the System Man-

agement Bus Specification, Rev 1.0.

The SMBus interface is used to read and write the registers in the device. The register set is shown in Section 5.3.9,

"Internal SMBus Memory Register Set," on page 21.

5.3.1

BUS PROTOCOLS

Typical Write Byte and Read Byte protocols are shown below. Register accesses are performed using 7-bit slave

addressing, an 8-bit register address field, and an 8-bit data field. The shading indicates the Hub driving data on the

SMBDATA line; otherwise, host data is on the SDA/SMBDATA line.

The slave address is the unique SMBus Interface Address for the Hub that identifies it on SMBus. The register address

field is the internal address of the register to be accessed. The register data field is the data that the host is attempting

to write to the register or the contents of the register that the host is attempting to read.

Bit Number

Bit Name

Description

7:0

HC_MAX_C_SP

Hub Controller Max Current Self-Powered: Value in 2mA increments that the

Hub consumes from an upstream port (VBUS) when operating as a self-

powered hub. This value includes the hub silicon along with the combined

power consumption (from VBUS) of all associated circuitry on the board. This

value does NOT include the power consumption of a permanently attached

peripheral if the hub is configured as a compound device.

Note:

The USB 2.0 Specification does not permit this value to exceed

100mA

A value of 50 (decimal) indicates 100mA, which is the default value.

Bit Number

Bit Name

Description

7:0

HC_MAX_C_BP

Hub Controller Max Current Bus-Powered: Value in 2mA increments that the

Hub consumes from an upstream port (VBUS) when operating as a self-

powered hub. This value includes the hub silicon along with the combined

power consumption (from VBUS) of all associated circuitry on the board. This

value does NOT include the power consumption of a permanently attached

peripheral if the hub is configured as a compound device.

A value of 50 (decimal) indicates 100mA, which is the default value.

Bit Number

Bit Name

Description

7:0

POWER_ON_TIME

Power On Time: The length of time that is takes (in 2 ms intervals) from the

time the host initiated power-on sequence begins on a port until power is good

on that port.