mbed 1-wire EPROM driver (DS2502)

I wrote some code for my mbed to read and program the memory contents of 1-wire EPROMs like the DS2502. It should work with any device that responds to the same commands. The code can read ROM, status registers and memory pages, and write to the status register and memory pages. I also incorporated support for cyclical redundancy checks since the devices aren’t erasable. I had to build an external circuit for the 12 volt programming pulse to protect the mbed signal pin. If you only need to read you don’t need this, but it is required if you want to program data. Download link to the project source files is below.

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Friday, October 5th, 2012 Electronics 11 Comments

Flash a monitor’s EDID with an mbed and RealTerm

If you’ve ever setup ATI’s Eyefinity with bezel correction or connected your computer to a TV you know what this is about. Bad EDIDs can be missing supported resolutions, or report an incorrect screen size. In my case bad EDIDs prevented me from enabling┬ábezel correction on┬ámy Eyefinity three monitor setup. This is because ATI coded their Catalyst drivers to read the EDID data directly from the monitors instead of the windows registry, where bad data can be fixed more readily with an EDID_OVERRIDE key.

DVI and mbed

EDID is Extended Display Identification Data. It’s what makes your monitor “Plug and Play”. When you plug a monitor into your computer, the monitor communicates data about itself to the computer over the DDC bus, which is an I2C bus. For a DVI connection, the I2C data and clock lines are on pins 6 & 7. Usually you would flash your monitor’s EDID while it’s hooked up to your PC with a program like Powerstrip, but you have to buy the registered version of powerstrip to have that functionality. Additionally, revision 3 of the EDID specification requires the EDID to be write-protected. That means to flash the EDID with Powerstrip you need to figure out the manufacturer’s sequence for temporarily unlocking the EEPROM. Something like turning the brightness and contrast to zero, then power cycling while holding the menu button, etc. I didn’t feel like messing around with that so I just took the monitor apart. › Continue reading

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Tuesday, April 19th, 2011 Electronics 1 Comment