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Topic: SSD1289 : question about the RD pin (Read 6 times) previous topic - next topic

guix

#10
Dec 16, 2012, 01:32 am Last Edit: Dec 16, 2012, 02:23 am by guix Reason: 1
Hello pYro, I am lazy! No I didn't do it yet, because I still haven't bought a soldering iron... :)

But, I'm almost sure it will work, because the guys who did the ArduCam use it to save a .bmp file from the display's GDDRAM (using a very similar display)

As for the Flash chip, I believe we need a SST25VF chip, especially the 16 Mbits version, SST25VF016B (also exist 32 and 64 Mbits versions of this chip, so in theory it could work too!), can be found on ebay for not much :) I would like to try, but I'm affraid I have no idea how to make it work, I can't really understand datasheets timings etc..

Edit: changed "MB" to "Mbits"..I have misread :)

pYro_65

Those flash chips look nice and easy to use. They are fast, with an auto address counter, could be very useful in a separate circuit to speed up sprite drawing. They would be nice on the shield for simple storage also. As I'm writing an 'animation capable' library for the screen, I will definitely look into testing one out.

Regarding the RD pin:
How would you connect the pins? Would you connect a digital pin on the 3.3v side or RD side of the resistor? Or maybe disconnect RD completely from 3.3v?
I'm thinking maybe an NPN on the RD side to pull RD low, the 3.3v sets the high.




MarkT


Hello, I have Sainsmart's 3.2" TFT display and adapter shield for Arduino Mega

I need to read data from GDDRAM, (to retrieve pixel color), in order to do that, I need to use the RD (Data Read) pin..which unfortunately isn't useable, look this picture:



Yes that's correct - the RD line must be wired high in serial mode (SPI) - you can't read except in one of the parallel modes.  This is
explained in the datasheet in "Table 2 Pin Function Description".

From what I can see of that adapter it uses the SPI bus - if so then you can't read the graphics memory.
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guix

#13
Dec 17, 2012, 01:37 am Last Edit: Dec 17, 2012, 01:41 am by guix Reason: 1
That resistor is only used by the RD pin, so yes I would remove it, and then 2 choices:

1- (Yellow line) Solder a wire from RD pin to pin D42 or whatever (pins D42 to D49 are unused).
2 - (Red line) Solder a wire from the pad of the (now removed) resistor to pin D42 or whatever.



I prefer the second solution :)

But will it work... What I don't understand is, why is there a 10kohm resistor here? And why on 3.3V and not 5V? Maybe the RD pin will not support 5V from D42? I can't find anything about this in SSD1289 datasheet...

Is a pin in HIGH state as soon as it receive voltage (or current?) that is greater than 0 ?




Yes that's correct - the RD line must be wired high in serial mode (SPI) - you can't read except in one of the parallel modes.  This is
explained in the datasheet in "Table 2 Pin Function Description".

From what I can see of that adapter it uses the SPI bus - if so then you can't read the graphics memory.


The SPI pins are used only by the SD card reader (on the back of the display, it's completely unrelated to the SSD1289). I believe the display use the mode "MPU Parallel 8080-series Interface" so I think no problem to use the RD pin :)

MarkT

Ah good - the 4 highlight traces suggested SPI to me on a quick glance.   If the board supports both SPI and parallel modes that
could explain the decision to hard-wire the RD line (requirement for serial). 
[ I won't respond to messages, use the forum please ]

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