Integrated USB 2.0 Compatible 3-Port Hub

Datasheet

SMSC USB2503/USB2503A

23

Revision 2.3 (08-27-07)

DATASHEET

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 SMSC 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 SMSC 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 24. Reference the System Management 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 25.

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.

Note:

Data bytes are transferred MSB first (msb first).

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.