E-Edid Support For Cable Supply Mode; Supply; Transitioning From Cable Supply Mode - Analog Devices ADV7850 Hardware Manual

Function
edid_d_enabled
0 
1
Notes:
• When the internal E-EDID is enabled on more than one port (for example, Port A and Port B), the corresponding enable
controls (for example,
fastest calculation of the checksums.
• If the internal E-EDID RAM is enabled for one specific port (for example, Port A), an external E-EDID storage device should
not be connected on the DDC bus of that port.
• The internal E-EDID can be read by Current Address Read sequences on the DDC ports.
• The ADV7850 supports the segment pointer, which is set at device address 0x60 through the DDC bus, and used in combination
with the internal E-EDID address (0xA0) to access the internal E-EDID.

E-EDID Support for Cable Supply Mode

7.5.1
The ADV7850 can support internal E-EDID access when no system power is present by using the +5 V supply available on the HDMI or
VGA cable, if present. (Refer to Section
E-EDID available to an HDMI source. This provides compatibility with HDMI transmitters that require the E-EDID to be available when
the system is powered down.
In cable supply mode, the part operates in a very low power state with only the minimum of internal circuitry enabled for the internal E-
EDID. This allows the E-EDID/Repeater controller to load the E-EDID image from an external SPI EEPROM into the internal E-EDID
RAM. The E-EDID/Repeater controller also updates the SPA of each port (refer to Section 7.11), computes the required E-EDID
checksums, and enables the internal E-EDID.
7.6 5 V SUPPLY
The ADV7850 can receive power from the +5 V power signal line of an HDMI cable(s) and/or a VGA cable. The ADV7850 has an
internal +5 V regulator. The output of this regulator supplies power to the E-EDID/Repeater controller, internal ring oscillator and
internal E-EDID RAM. It also supplies a 3.3 V external output onto the pin VDD_EEPROM, which can be used to power an external SPI
EEPROM. This allows a system containing the ADV7850 to present an E-EDID image to the HDMI source even if no system power is
available.
When this cable supply mode is initiated, the internal E-EDID is automatically configured and the part loads its internal E-EDID with the
information in the SPI EEPROM, and internal E-EDID is enabled on all ports.
Note: The external SPI EEPROM used in a system should consume no more than 5 mA of current. This is required in order to ensure no
more than 10 mA in total is drawn from the +5 V HDMI cable supply.

7.7 TRANSITIONING FROM CABLE SUPPLY MODE

If the part starts in cable supply mode and then transitions into normal operation mode (that is, full system power available), the
information in the internal E-EDID is not overwritten. The internal E-EDID remains active on the HDMI port(s) for which the E-EDID
has been accessed. This prevents disturbing E-EDID read requests from HDMI sources connected to the ADV7850.
edid_pwrsw1p8[1:0], Addr 68 (HDMI), Address 0x71[1:0]
Controls the switch related to EDID power domain taking the system or the cable supply. Dedicated control for the 1.8V domain.
Rev. A May 2012
Description
Disabled
Enabled
man_edid_a_enable and man_edid_b_enable) should be set to 1 in one single I
7.6 for more details.) Using this feature, an application that integrates the ADV7850 can make its
144
ADV7850
C write. This ensures the
2