VGA PSP Screen

[psppunk]

Okay, so people have made the PSP output VGA by using a Triple-8bit 80mbps Digital>Analog Converter
but now its time to do it backwards, by letting the PSP screen accept VGA input....

im thinking with 3 of these http://focus.ti.com/docs/prod/folders/print/ads831.html and some careful soldering it shouldnt be too hard

only thing i need to know is....:
What to use on the clock line
Ive heard of pulling lines high and low but never really understood that, can someone shed some light as to what exactly this means? because pins 11 and 12 seem to need this

[gr8npwrfl]

What do you intend to do with the analogue to digital converters ?

If you are thinking that you can drive the lcd screen with these you can't do that.

You have to have an LCD driver chip to generate all the timing and signals the LCD needs
to be able to generate a picture.

These analogue to digital converters will only take the VGA video signal and convert it to
digital. You have to combine the digital information with the vertical and horizontal sync
signals to generate the timing to know when the data you are converting is valid. These
signals will not be valid during sync and retrace time.

If you have an LCD controller you need to gate the signals from the converters to the
controller at the correct time and bit positions to get the correct data displayed.

Have you ever taken an LCD TV apart ?

If you throw away the power supply and the turner, but kept the video inputs, that is
what you would be building, but it has to have the timing specs that match the display
you are using.

OR have I missed the boat on what you are trying to do ?

[psppunk]

no you have not missed the boat, that is exactly what i am trying to do, and it isnt impossible
the psp screen has h and v sync, so does a computer outputting vga

i only need to know what to do with the clock/timing pin and it will work
im thinking either a capacitor, a crystal, or something with the syncs

[Blizzrad]

Psppunk, you are correct that it is not impossible, but you are greatly oversimplifying the required process (as I understand it). The horizontal and vertical sync signals pulse at set frequencies to signify the beginning of a new line or frame respectively. Each line consists of a set number of pixels which are drawn one by one, left to right, at the speed of the pixel clock (9 Mhz in the LCD's case). There are also the horizontal and vertical blanking intervals which occur for a set number of clock cycles between each line/frame. All of this makes up the signals timing, and it is very important if the signal is to be displayed as anything but a scrambled mess.

As gr8npwrfl said above (I can't even think as fast as he types ), converting the VGA RGB signals from analog to digital does not address the important differences in signal timing. To do this you will need some type of powerful programmable logic device like a CPLD/FPGA or other LCD controller board. If you are serious about this project I suggest searching the forums over at sparkfun.com. They carry the PSP LCDs as a display for electronics projects, and there are several threads in the forums regarding the required hardware to drive them. There is also another short thread discussing this same idea here.

[psppunk]

=] nice! a helpful response

well i was looking at the datasheet for the chip i linked to and it seems to do just that, why dont you take a look
amirite or is it doing something completely different with the clock line?

[Blizzrad]

It looks like the clock input determines the rate at which the incoming analog wave is sampled and digitized. The chip does not manage the sync pulses or account for the overall timing differences between VGA and the PSP's LCD. This is just speculation, I would love love to be wrong about it, but I can't see this working by itself.

[psppunk]

can you explain to me what exactly you mean by timing differences?
you know more than i do on this subject and id really like to know

[gr8npwrfl]

Small Portion of one of my LCD Controller manuals

MECHANICS OF AN LCD PANEL

An LCD panel comprises a matrix of pixels (picture
elements), divided into red, green, and blue “sub-pixels”.
Each sub-pixel is driven by a small transistor. Typically,
LCD panels have internal row and column
drivers, much like DRAM. A row is selected by the row
driver, then the column driver sequences through each
of the columns. After each of the columns has been written,
the row driver selects the next row and the process
repeats. The VSYNC signal resets both row and column
drivers to the upper left pixel. The HSYNC causes the
row driver to step to the new row. The clock sequences
the column driver through each of the pixels, with each
clock edge latching data values for the red, green, and
blue sub-pixels. These values drive a form of D/A converter
to store an electrical charge in a capacitor in each
sub-pixel which controls the drive of the transistor; this
in turn controls the brightness of the sub-pixel. A redgreen-
blue color mask is used to filter the light from
each sub-pixel to form its corresponding color.

Like a DRAM, an LCD panel must be constantly
refreshed or the image will fade. Most TFT LCD panels
work fine when refreshed around 60 Hz. To refresh the
charge in each of the sub-pixels, the entire image data
must be rewritten to the panel. This is one the functions
performed by the LCD controller. The image data is
usually held in a section of main memory called a frame
buffer. This means that the LCD controller is constantly
accessing data from the frame buffer and sending it to
the LCD panel. Depending on the resolution of the
panel, transferring this refresh data may have a significant
impact on bus bandwidth. This is why processors
utilizing low bandwidth buses cannot be used to drive
large TFT displays.
Each location in the frame buffer corresponds to a
pixel on the LCD. The value in the location determines
the color displayed for that pixel. See Figure 2. The size
of the frame buffer depends on two things: the number
of locations needed, and the size of each location.
The total number of locations needed is determined
by the panel resolution. For instance, the resolution of

the Sharp LQ050Q5DR01 panel is 320 × 240 pixels.
Therefore 320 × 240 = 76,800 memory locations will be
needed in the frame buffer — one for each pixel.
The size (or number of bits) of each location is
slightly more complicated. The size depends primarily
on the number of individual colors needed. A larger
number of different colors will require more bits (or ‘bits
per pixel’ (BPP)) to define it. For instance, 16 bits can
describe 65,536 different colors. Therefore a display
design employing a 320 × 240 panel displaying 65,536
different colors requires 76,800 16-bit locations
(153,600 bytes) and 16 data lines from the processor to
the panel. This assumes, of course, that each bit can be
passed to the LCD panel on its own individual data line.
TFT panels typically have an input of at least 6 bits of
red data, 6 bits of green data, and 6 bits of blue data. A
panel with 6 red, 6 green, and 6 blue data lines is termed
a 6-bit panel. If the processor or LCD controller doesn’t
drive as many data lines as the panel requires, use the
data line configuration shown in Figure 3 or Figure 5.

This is an excerpt from one of my controller manuals

All of the timing and clocking is programmed into this
controller just to make the LCD work. The timing is in the
nanoseconds to make sure you are talking correctly to
an individual pixel.

You are missing many parts to the information that is
needed. How will you tell the A/D when to sample the
data from the inputs ? If you are 5 nanoseconds one
way or the other you will not have the true value you
are trying to read ?

How long the wires you interconnect the parts with
will change the circuit timing.

You will need a pixel clock, sample clock, vertical blanking
interval timer, horizontal blanking interval timer, just to
name a few.

[psppunk]

well if it works then i guess itd be somewhat of a miracle

im kinda going to wait for blizzrad's response though, he explains things in a way thats easy to understand =]

[gr8npwrfl]

Sorry for getting too technical.

I have designed LCD interfaces before and I just know all the timing.

I thought that part would be easy enough to see what was involved

[Blizzrad]

The excerpt gr8npwrfl posted is actually one of the most straightforward and concise explanations I have seen on this subject.  The technical aspects of how each pixel produces a given color is good to know but the most important bit to understand is:

The VSYNC signal resets both row and column
drivers to the upper left pixel. The HSYNC causes the
row driver to step to the new row. The clock sequences
the column driver through each of the pixels, with each
clock edge latching data values for the red, green, and
blue sub-pixels.

PSP LCD timing is:

480 active pixels per line + 2 for front porch + 2 for back porch + 41 for horizontal blanking = 525 pixels per line
272 active video lines + 2 for front porch + 2 for back porch + 10 for vertical blanking = 286 lines per frame
286 lines x 59.94 frames per second (59.94 Hz vsync) = 17,142 lines per second (17.14 kHz hsync)
525 pixels per line x 286 lines per frame = 150,150 total pixels per frame
150,150 x 59.94 frames per second = approx 9,000,000 (9 mHz pixel clock)

This is the allowed timing for the PSP LCD, the datasheet for the LCD shows a waveform diagram on page 13 which helps to illustrate the above descriptions. Timing for other signals like VGA video depends on the resolution and refresh rate of the signal. This page has a calculator with presets for various common video standards which will show the differences in signal timing. Unlike LCD computer monitors and TVs, the PSP LCD was not intended to take input from a range of different devices, and therefore does not contain the necessary hardware to scale various signals to it's native resolution. It relies on the controller to send it video in accordance with the above timing specifications.

[psppunk]

well i sort of understand
i was under the assumption that the clock pin handled the timing in the signal

if it makes any difference i have a hacked video card driver that lets me set my sync and resolution to any value i can key in
*shrugs* probably not

i just dont see the point of buying an entire  "mini linux computer" just to use a screen

[ryan0]

on the gp2x the h-snc and v-sync signals were slightly different to that of a tv,and placing a 220uf capacitor on there smoothened it out so it could output to a tv,forgive me if i'm wrong

[psppunk]

that is correct, it works on psp too, but thats not what were talking about =P

[ryan0]

that is correct, it works on psp too, but thats not what were talking about =P

oh lol,sorry I'm not too good with lcd's and vga etc. etc. just thought that it might have helped lol 

[gr8npwrfl]

If you want a second display there are many serial LCD devices.

You could plug it into the headphone serial port and that would interface for you.

The mini linux computer is performing tons of other conversions not just running a
second display. It is doing mass storage, usb host functions and interfacing.

[psppunk]

well everything ive seen so far says to get that little thing =/ i know it does more, and thats actually the problem

what could be used to get vga video onto the psp screen?
something that does nothing else, but convert the video for use on the screen

[gr8npwrfl]

Panasonic makes a single chip solution.

The AN2546 is used in automotive applications to take composite video or rgb video and drive a
small size LCD screen.

You will also need another chip to isolate the PSP driver lines from the display.

[psppunk]

eh, i just woke up, isolate the driver lines?

[gr8npwrfl]

if you want to run the same display on both you will have to isolate the driver lines on the display.

On way lets the chip run the display the other way lets the PSP run the display.

A switch point on the input plug that switches the LCD to run from your composite
driver.

When the composite connector is plugged in the display is run from the new chip
When the connector is unplugged the display is run from the PSP

[psppunk]

ok, i shouldnt need that then, this is just a spare lcd, and i can solder straight to the flex

[gr8npwrfl]

Get an old motherboard and steal the connectors from it.
Solder the connectors to your breadboard and you will not have
to solder to the cable

[psppunk]

its ok, soldering to the cable is easier for me =] idk why
thanks for all your help man 

[gr8npwrfl]

No problem, always here

[tonycjr23]

Gr8npowerful man i love reading your replys because i ALWAYS learn something you are just a wealth of knowledge and a true asset to this board

[gr8npwrfl]

thank you for the compliment

[Blizzrad]

well i sort of understand...

I know what you mean, I have been looking for a way to do the opposite of this (PSP -> VGA) for a while now and am only slowly beginning to grasp how these kinds of video signals work, and how they might be converted. Most of the documentation online regarding this subject (datasheets in particular) assumes that the reader already has a level of understanding consistent with an education or profession in the field.

i was under the assumption that the clock pin handled the timing in the signal...

I guess in a way it does, since everything revolves around the timing of the pixel clock, it just also needs the sync pulses to define the boundaries and refresh rate of the image.

if it makes any difference i have a hacked video card driver that lets me set my sync and resolution to any value i can key in
*shrugs* probably not

i just dont see the point of buying an entire  "mini linux computer" just to use a screen

That sounds like it would make a big difference, providing you can get the timing within the accepted range. If you can do this, then you might be able to get away with using only the ADCs like you had planned. I have heard of this being done to create a 15 kHz RGBS signal for sending video from a PC to a PSOne LCD. Which graphics card and drivers are you using?

If you are referring to the responses in the sparkfun thread regarding the mini linux computer, I completely agree. While using a mini linux computer to drive the LCD might work, it would only make sense if you actually want a portable linux computer, not a portable video monitor.

well everything ive seen so far says to get that little thing =/ i know it does more, and thats actually the problem

Which sources pointed you towards using the ADCs? I am interested because I too have read things online pertaining to video conversion that seem to totally conflict with what I have read elsewhere. I would like to read more about this if you have any links.

Panasonic makes a single chip solution.

The AN2546 is used in automotive applications to take composite video or rgb video and drive a
small size LCD screen.

Looking at the datasheet, it seems this chip was designed to interface with normally white LCDs, whereas the PSP LCD is normally black. I also don't see where it has the outputs necessary for a parallel 24 bit interface like the LCD requires, but maybe I am mistaken. I don't think this chip would work for what we want it to do, but perhaps another like it would. If a simple single chip solution could be found, it would make a lot of people happy over at the BenHeck.com forums (among others), they do a lot of portable console hacking over there, mostly based around the much bulkier PSOne LCD.

As far as the soldering is concerned, I think using a spare zif connector to make a breakout adapter is a smart idea because if something goes wrong and the screen needs to be replaced (always possible with a project like this) you won't need to redo all of your wiring, although soldering directly to the LCD ribbon is the quicker and easier method.

[gr8npwrfl]

I will find you a controller that will work this weekend. I have the documents on so many I did not see it was for a
white screen.

[mark_tarugs]

is there anybody who could help me out i checked my psp opened it and removed the lcd but when i placed it back the backlight was gone what do i do to bring it back

[ApheX]

Jesus, Dude. this topic is very much dead. I wouldn't make a habit of that if i were you. But seeing as you need help......

Ok, first off, check to make sure the backlight ribbon is connected properly. it might just be lose. If not then it might be that a fuse on the mobo has blown or the backlight itself is dead. I would think the backlight is the problem and they can be replaced.

Why were you taking the psp apart? were you modding the console?