JAJSGX4 February 2019 TUSB8044A
ADVANCE INFORMATION for pre-production products; subject to change without notice.
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 controls whether or not Billboard is presented to the Host system. When BBEN pin is high, the Billboard is presented to the Host system.
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 is high, BBEN must be transitioned low, BBbmConfigured[1:0] pins updated to reflect new status, and then BBEN 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.
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.
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 + BBString2Len size must be <= 480 bytes, or < 480 if # characters in string 1 is odd, because string 2 must start on an address that is a multiple of 4 (bytes). |
1-byte | 0x2D | 0 = use default string in ROM | BBString2Len. # of Unicode characters (2 bytes each) in string 2. |
480 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. |
“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/. |
The TUSB8044A supports the Billboard Alternate Mode Capability Descriptor. The dwAlternateModeVdo field in the descriptor defaults to 0x00001C45 to align with DisplayPort Alt mode VDO with capabilities described in Table 5. The default can be changed from OTP or EEPROM/SMbus. All dwAlternateModeVdo bits are accessible from the EEPROM/SMbus but only some of the bits are accessible thru OTP.
Bit(s) | Default Value | Description | OTP Configurable |
---|---|---|---|
1:0 | 01b | 00b = Reserved
01b = UFP_D capable 10b = DFP_D capable 11b = Both UFP |
Yes |
2 | 1b | Supports DP Standard signalling rates | No |
5:3 | 000b | Reserved | No |
6 | 1b | 0b = DP Interface presented on USB-C plug
1b = DP Interface presented on USB-C receptacle |
Yes |
7 | 0b | 0b = USB 2.0 signalling may be required in DisplayPort configuration
1b = USB 2.0 signally not required in DisplayPort configuration |
Yes |
9:8 | 00b | Reserved | No |
12:10 | 111b | DFP_D pin assignments supported.
000b = DFP_D pin assignments are not supported. xx1b = Pin Assignment C is supported. x1xb = Pin Assignment D is supported. 1xxb = Pin Assignment E is supported. |
Yes |
17:13 | 00000b | Reserved | No |
20:18 | 000b | UFP_D pin assignments supported.
000b = UFP_D pin assignments are not supported. xx1b = Pin Assignment C is supported. x1xb = Pin Assignment D is supported. 1xxb = Pin Assignment E is supported. |
Yes |
31:21 | 00000000000b | Reserved | No |