PSP LCD Screen on Propeller
Brandon C.
Posts: 106
Hi everyone! I guess you probably don't remember me. I joined back in November 08 with a bunch of questions about the Propeller chip.
Anyway, I still haven't bought it. But i was wandering how you would interface something like this to the propeller chip? would you need anything extra?
Thanks!
Brandon C.
Anyway, I still haven't bought it. But i was wandering how you would interface something like this to the propeller chip? would you need anything extra?
Thanks!
Brandon C.
Comments
At the very least, you'd need a 2.5V regulated supply. As it stands, you'd probably need to use nearly all of the Propeller's I/O pins to drive it unless you build an interface with some latches to hold pixel values for each of the colors. I'm sure you'd need some way to control the backlight which I presume is LED-based (I could be wrong). You probably will need some kind of output buffer or at least protective series resistors for the signals to the display since they're supposed to be 2.5V logic signals and the 3.3V outputs of the Propeller could damage the display. If you use latches, you may be able to find some that will run off 2.5V and accept 3.3V logic inputs and that will simplify interfacing.
The page is in german. But you get the idea. In those forums there are quite a bit of people that has it already working.
Edit: mike almost beat me to it
The Backlight is 28V DC. you'll need some sort of a buck regulator.
The 40 pin connector is very small pitch (0.50mm)....very difficult to solder.
Memory is a big concern, 3 bytes per pixel X 480 pixels wide X 282 pixels high = 406080 bytes if you wanted a full 24 bit color image. It must be streamed to it 60 times per second.
well.... Let's just say I wouldn't recommend it as your first Propeller project.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Brian
uController.com - home of SpinStudio - the modular Development system for the Propeller
PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!
SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
Here's my current plan:
Brains: Altera MAXII in a 100 QFP package. 570 LE's would be plenty and it would leave it with enough room for a bunch of features.
Memory: Cypress 4Mbit SRAM with 10ns Taa
LED: Linear tech LED boost driver for the 7 LED back light with pwm input for use with a Propeller counter
Interface: One of the hardest parts. It would consist of a 9 bit data bus, clock, address/data,back light PWM, and direction pin.
The CPLD would constantly read from the SRAM and display whatever it contains on the screen. This saves a lot of work on the propeller side. Writing data to the SRAM would also be handled by the CPLD through the data bus.
A 9 bit bus sounds kinda weird, but it allows a bunch of possible features to be added. Instead of writing to the entire screen over and over, you can just write to a selected portion at a time. The way this would work is that you send the x start, x stop, y start, and y stop to the screen over the data bus. This sets up a box where the controller will write to the memory. When you send pixel data, it will start at (x start, y start) and run all the way until you reach the x stop, where it will wrap around to the next line and back at (x start,y start+1). Once it reaches (x stop, y stop), then it wraps around to (x start, y start). This allows you to easily draw portions of the screen over and over without having to address them again. The address/data pin would be used when you want to enter a new address to write data to the memory.
Because of the pixel dimensions of the screen, a 9 bit bus is required to send the addresses to the controller. Pixel data is sent 1 byte at a time in RGB format, with each pixel 3 bytes large. While pixel data is being sent to the screen, the 9th bit is not used. My plan was to make this a transparency bit, where when active, the pixel data present on the pins is ignored, and the old value is kept. This would make it super simple to draw transparent images on top of backgrounds without having to read from the screen memory. A read option would be available, but I haven't figured out how the pin directions would be handled.
On the prop side...
The 9 bit bus would make data transfer very quick, allowing fast refresh, even for the entire screen. If you are refreshing only a part of the screen, then you could easily stream video to it. The only problem is can the prop decode video? I'll wait for the Propeller II to figure that one out.
The back light is driven by a LED boost regulator with a convenient PWM input. It has a fairly wide Vin of 3-10V (I think), and the PWM could be fed by any counter on the propeller.
The MAX II also has a wide input of 1.8 to 3.3V with 5V tolerant pins.
One really annoying thing is that the SRAM only accepts 3.3v. The LCD already requires 5V and 2.5V, so another voltage is more of a hassle. In the sharp datasheet, it does say that the LCD inputs have a max input of 3.3, so I may be willing to push this for the sake of simplicity.
All in all, this would be a fun project for me, and it may be marketable. Would anybody be interested in a shiny, full color LCD add on to their project? The whole thing would run for about $100, including LCD. I still have to develop it, but it would be nice to know I may have buyers.
Kevin
P.S: Did I hijack anything here?
http://www.sparkfun.com/commerce/product_info.php?products_id=8539
I can't really tell why it is so expensive though. Does it have a built in propeller chip or something?
A little lower in price, and a little larger screen, and there are objects available in the Object exchange obex.parallax.com/ to drive it.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Brian
uController.com - home of SpinStudio - the modular Development system for the Propeller
PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!
SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
The unit you found from SparkFun does have a Propeller built-in. It also has a microSD card socket. It's very nice although quite small. The unit that parts-man73 references has a little larger screen and uses a custom controller rather than a Propeller. This has a serial interface and can be used with both a separate Propeller and the Stamps.
Thanks parts-man, Ale, kevin, Mike.
I look forward to purchasing a Propeller.
http://www.embeddedartists.com/products/displays/lcd_qvga_32.php
I currently wouldn't buy an expensive OLED-display. They are brilliant, but with age they get worse and without experience I'd prefere well known LCD displays.
The other option was the PSP display because you can get it as an replacement for 30 something Euro. Wouldn't buy it for $100 but maybe it's a nice task for the next CPLD or FPGA project.
Post Edited (MagIO2) : 5/11/2009 3:52:39 PM GMT