[Arm-netbook] Microdesktop v1.7
richard.wilbur at gmail.com
Wed Jul 18 01:49:56 BST 2018
1. Make VESA DDC lines conform to VESA DDC spec. (VDD=5.0V, I2C
2. Respect VREFTTL in the range of 3.3-5.0V on EOMA side of VESA DDC lines.
3. Respect EOMA requirement that all lines except EOMA I2C be tri-stated
at power on.
1. Connect pull-up resistors for VESA_SDA(R8) and VESA_SCL(R12) to
VESA_PWR (+5.0V) instead of VREFTTL. Maximum current requirement on
VESA_PWR is ~670uA.
2. Implement circuit in attached
diagram[EOMA_I2C_circuit_sketch_small.png] on each of SDA and SCL. I have
attached a spreadsheet[EOMA_I2C_VESA_calc.pdf] showing how this
accommodates the I2C signalling for VDD=3.3V=VREFTTL and VDD=5.0V. It
also accommodates the EOMA68 VREFTTL input levels by not allowing the EOMA
side of the signal to exceed one Schottky diode drop(0.3V) above VDD=3.3V.
3. Enable the current limiting regulator (SY6280) for VESA_PWR (+5.0V on
VGA pin 9) with latch of LCDDE when it first goes active (line coming from
More information about the arm-netbook