VGA external on OLPC

John Watlington wad at
Tue May 13 11:11:02 EDT 2008

On May 13, 2008, at 2:29 AM, Dietmar Stölting wrote:

> Hi all, after reading
> the-xo/
> I am sure, that it is possible to integrate a VGA external  
> connector for the OLPC. On the Prototype-A motherboard layout there  
> was such an external VGA connector, but on G1G1 version it is gone.
> I am a teacher and it would be very good for projection with a  
> beamer or if your LCD is broken, to have such an external VGA  
> connector.
> My problem is, that I have no schematic or a good photo of both  
> sides of the Prototype-A motherboard. You can read in the Geode LX  
> databook, that the Geode LX chip offers direct VGA support and  
> connection. But some parts of the Prototype-A motherboard have gone  
> in G1G1 version and so I cannot see, which direct lines from the  
> processor has to be used for the direct VGA support. Pin 1,2,3 are  
> used for the RGB signal on the G1G1 layout, and pin 13 seems to be  
> Hsync and pin 14 Vsync. I do not know, what is the use of pin  
> 4,9,12,15, because they are also wired on the G1G1 version.
> Pin 5, 6,7,8,10,11 are not connected on the G1G1 version and I  
> think, that this was the same for the Prototype-A motherboard  
> layout. But still there must be the lines direct to the Geode  
> processor from the Prototype-A layout. They only have to be found  
> (recogniced) via a good photo of the Prototype-A layout (both  
> sides). Please send me your photos and rtell me, what you think  
> about my idea,
> Dietmar

You are not the first to think of this, nor will you be the first to  
try it.
We don't recommend it.


[Additional information you will need if you choose to proceed]

Components that were depopulated on C2 (MP machines) needed to support
VGA output are:

U2, U3: 74AHCT1G125GW    (sync drivers)
C152:    0.1 uF
R1, R2, R3:  75 ohm

To support the VGA I2C link (UART 2 on the CS5536 southbridge):
R122, R123:  10K
Q7, Q8:  2N7002
R115, R116:  10K
D6:  CH501H-40PT  (just about any schottky diode should do, this is  
       in the +5V supplied to the monitor)

Good luck finding that VGA connector, I don't have a part number for it.
The pinout is attached.
The signal/pin mapping is:
Red - 1
Green - 2
Blue - 3
NC - 4,11
GND - 5,6,7,8,10
VSYNC - 14
HSYNC - 13

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