*Edit 2009*
To avoid leaving behind a pile of misinformation for others to step in, I wanted to come back and edit this old thread to save anyone else from wasting their time. The thread was originally started to discuss a set of schematics found on another website for building a circuit that would convert 24-bit 480x272 digital video from a PSP to standard VGA by tapping directly into the LCD lines. Some things about the circuit didn't make sense, namely it's absence of any logic to reconstruct the signal timing, and unfortunately it turns out the schematics were just a hoax. For anyone looking for useful information regarding PSP LCD video timing and adapting signals to/from it, the forums at sparkfun.com are a good resource, these threads in particular are useful: 1 (http://forum.sparkfun.com/viewtopic.php?t=7423&postdays=0&postorder=asc&highlight=psp&start=0), 2 (http://forum.sparkfun.com/viewtopic.php?t=8655&highlight=psp), 3 (http://forum.sparkfun.com/viewtopic.php?t=10856&highlight=psp), 4 (http://forum.sparkfun.com/viewtopic.php?t=10481&start=15&postdays=0&postorder=asc&highlight=psp)
I'm afraid a VGA monitor wouldn't display that...
Well mine sure didn't :D, but this is why I am so puzzled by how this guy was able to do it ???. The monitor he used is a LG 2323T (http://www.superwarehouse.com/LG_Flatron_L2323T_23_LCD_Monitor/L2323T/ps/437286) LCD.
Sometimes LCD's have scalers that are more lenient.
CRT's sure aren't though.
As far I know the DAC don't need to know what's going with the sync lines.
You see ... All you need is a strobe to tell the DAC to latch the signal, and the schematic has both a clock and a latch signals.
You can just forward the sync signal to your monitor from the PSP LCD ribbon, if it does require sync.
Right, I understand this. But according to what is implied in the thread, the DAC should also generate csync which is compatible with standard displays. Otherwise there would still be the same timing problems as with the first method. Quoting SpectroPlasm from page 12 of the thread:
"I think it's easier to use the chip tbh since it double as a built in sync doubler too (it regulates the hsync to be compatible with the output host signal)."
This is what is confusing to me about the second schematic, because I don't see anything in the datasheet about how the HI-1178 handles this sync generation. Any ideas? (and thanks for the replies and help by the way)
It's possible if the DAC chip has logic to reconstruct the sync signal using the latch signal timing and the video clock.
Also by his schematics the output is YCbPr (Component Video) instead of plain RGB.
I tried to read the datasheet myself and failed to find any information. Still I believe it might be related to the blanking function mentioned on the datasheet. Anyway should it not work, just hook the sync signals from the PSP on the monitor.
The schematic labels the outputs as both YPbPr and RGB, but then in the comments it is stated that it outputs sync on green, so I'm assuming it's RGsB by default. He mentions the same thing you suggested about using the h and vsync straight off the ribbon as an alternative for non-SoG compatible monitors on page 8:
"...to werejag or the others who would like to bypass the SoG and use the native H-sync and V-sync frequencies just take it out of the first diagram i posted a while back"
The problem with this is by default the PSP timing is 480x272 59hz vsync and 17.1khz hsync, and I don't know of any VGA monitors which will display something like that. (apart from the LG 2323t apparently)