From 44d683521050b5ba48f367fb9cfffc6688d1318f Mon Sep 17 00:00:00 2001 From: Stefan Brüns Date: Mon, 1 Jan 2018 22:37:02 +0100 Subject: Add trace with Acer AL711 TFT behind DP-to-HDMI and HDMI-to-VGA adapters The HDMI-to-VGA adapter provides audio via a 3.5mm socket. This feature is announced using a CEA extension block. The DP-to-HDMI adapter (Type 1) shows up at i2c address 0x40. It just provides an identification register/eeprom, reading 'DP-HDMI ADAPTOR\x04'. --- i2c/edid/README | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) (limited to 'i2c/edid/README') diff --git a/i2c/edid/README b/i2c/edid/README index c49a9ea..422ec53 100644 --- a/i2c/edid/README +++ b/i2c/edid/README @@ -2,12 +2,15 @@ EDID ------------------------------------------------------------------------------- -The captures in this directory were taken from a VGA cable, connected to -various displays, as the EDID data was sent across the I2C bus. +The captures in this directory were taken from the DDC/I2C bus. + +For the two Samsung displays below, the logic analyzer was attached to a +VGA cable, which connects the computer and the display while the EDID data +was sent across the I2C bus. To decode these, set up a protocol decoder stack like this: - i2c -> i2cfilter -> edid + i2c -> edid Details: https://en.wikipedia.org/wiki/Extended_display_identification_data @@ -35,3 +38,21 @@ The logic analyzer used was a Saleae Logic (at 1MHz): 1 (black) SCL 2 (brown) SDA + +acer_al711_on_dp_dm_hdmi_vga.sr +------------------------------- + +This setup is somewhat more evolved, as it used a computer with a +dual-mode displayport (DP++), a DP-HDMI (Type 1) adapter, a HDMI DDC +breakout cable, a HDMI-VGA adapter, and a CRT screen with VGA input. + +The logic analyzer was connected to the DDC bus between the two adapters +above, i.e. on the HDMI connection. As the DP-HDMI adapter uses a level +shifter between DP and HDMI DDC busses, also the communication between +computer and the DP adapter is visible (the DDC busses on both side are +physically connected). The DP-HDMI adapter is visible at I2C address +0x40 and responds with the readonly identifier 'DP-HDMI Adaptor'. + +The HDMI-VGA adapter modifies the EDID contents from the VGA moniter, +it adds an CEA extension block at offset 0x80 and notifies the existence +of the extension block in the first block. -- cgit v1.2.3-54-g00ecf