TUSB8044AI datasheet(19/69 Pages) TI1

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TUSB8044A

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SLLSF92A – FEBRUARY 2019 – REVISED MARCH 2019

Product Folder Links: TUSB8044A

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8.3.4 USB2.0 Billboard

Integrated in the TUSB8044A is a USB2.0 Billboard device which complies to the “USB Device Class Definition

for Billboard Devices Version 1.21” specification. The billboard device is attached to the highest number

downstream port of TUSB8044A USB2.0 hub. The purpose of the billboard is to communicate Alternate Mode

status to the host system. The TUSB8044A supports only one Alternate Mode.

There are three pins, typically controlled by a USB Power Deliver (USB PD) controller, used to configure

TUSB8044A Billboard functionality: BBEN, BBbmConfigured0, and BBbmConfigured1. The pins are only used

when I2C mode is selected. If SMBus mode is selected, then TUSB8044A registers are used instead.

BBEN pin controls whether or not Billboard is presented to the Host system. When BBEN pin is high, the

Billboard is presented to the Host system. In SMBus mode, BillboardEN field in the Billboard Configuration

BBbmConfigured[1:0] pins map directly to the bmConfigured fields in the Billboard Capability Descriptor. These

two pins must be set to reflect the Alternate Mode status before BBEN is asserted high. If Alternate Mode status

changes after BBEN pin is high, BBEN pin must be transitioned low, BBbmConfigured[1:0] pins updated to reflect

new status, and then BBEN pin asserted high. For cases in which USB PD controller only has one available

GPIO to control TUSB8044A Billboard functionality, BBbmConfigured[1:0] pins should be tied to GND and BBEN

pin must be asserted when an Alternate Mode failure occurs. In SMBus mode, bbConfigured and BillboardEn

fields located in Billboard Configuration register performs this function.

In I2C mode, the TUSB8044A billboard capability descriptor fields can be changed using an external EEPROM.

At power-up, the unique billboard fields from external EEPROM are loaded into TUSB8044A billboard. Fields

controlled by EEPROM are described in Table 4. When an EEPROM is not used, the TUSB8044A’s default

values as indicated in Table 4 are used.

In SMBus mode, the TUSB8044A billboard capability descriptor fields can be changed by the external SMBus

master. The SMBus master can write to String1 starting at address 0x100 and String2 starting at address 0x1F0.

Please note if SMBus master writes data to address 0x2F0 through 0x2FF, this will overwrite data at addresses

0x1F0 through 0x1FF.

Table 4. EEPROM Billboard Capability Descriptor Map

SIZE

I2C EEPROM

ADDRESS

TUSB8044A DEFAULT WHEN

EEPROM NOT USED

DESCRIPTION

4-bytes

0x0F,0x0E, 0x0D,

0x0C

0x00001C45

AlternateModeVdo. dwAlternateModeVdo field for the

Billboard Alternate Mode Capability Descriptor.

2-bytes

0x28,0x27

0xFF01 (DisplayPort)

SVID.

2-bytes

0x2A,0x29

0x82EE

Billboard PID. Billboard and hub will share the same VID.

1-byte

0x2B

0x80

Billboard Configuration. When EEPROM used, this field

must be set to 0x80.

1-byte

0x2C

0 = use default string in ROM

BBString1Len. # of Unicode characters (2 bytes each) in

string 1. BBString1Len size can not exceed 120 characters

(240 bytes).

1-byte

0x2D

0 = use default string in ROM

BBString2Len. # of Unicode characters (2 bytes each) in

string 2. BBString2Len size can not exceed 120 characters

(240 bytes).

240 bytes

0x100

http://www.displayport.org

String 1. AdditionalInfoURL – required string descriptor

providing a URL where the user can go to get more

detailed information about the product and the various

Alternate Modes it supports.

240 bytes

0x1F0

“DisplayPort”

String 2. AlternateModeString – optional string to describe

the alternate mode, which may include a URL. From

Billboard spec, An example string is DisplayPort to VGA

adapter. For further assistance, see

http://help.vesa.org/dp-usb-type-c/.

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