I'm trying to modify an HDMI decoder board by Adafruit(https://learn.adafruit.com/adafruit-tfp401-hdmi-slash-dvi-decoder-to-40-pin-ttl-display/downloads) to work with an IPS screen that has a 51 pin connector. The adafruit board supports only 40 pins.

I've got the datasheet for the screen and while I have been able to decipher most of it, there are a few pins which I'm unsure about. I was hoping I could clarify some of it before going out and producing the PCB.

Here's the relevant part of the datasheet:

enter image description here

My questions:

1) Pin 39 - Does the reset pin need to be connected to ground? If it is active low, would connecting it to ground cause the device to keep resetting?

2) Pin 40 - Does low enable mean it is enabled by pulling to ground. I read if a CS pin is off it ignores the outside world for both inputs and outputs. Does this mean it should be connected to GND for the device to receive RGB data?

3) Pin 47-48 - The screen supports different interfaces but I need to use the RGB interface. Does this mean I should connect pin 47 & 48 to 3.3V so it reads as 1 for both and activates the RGB interface?

Also for reference here is the entire datasheet: https://www.scribd.com/document/383775532/4in-IPS-display


1) No. It's a pulsed input. From Figure 7.6.12, on datasheet, we can see that the pulse for RESX (pin 39) must be in low state for at least 10 us. Must be high for normal operation. Also, it's necessary to wait 5 ms after releasing the RESX pin before sending commands.

2) Depend. The CS signal (chip select) is used by i80 interface, but I think this same pin is renamed as SCEX when using the SPI interface.

3) Yes.

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  • \$\begingroup\$ Ok, this might be a stupid question but this pulsed input would be generated by the decoder board(TFP401) or my raspberry pi? I have no idea how to even begin to set these varying pulse requirements. Also, should I leave CS floating or tie to ground if I don't need to use the i80 or SPI interface? \$\endgroup\$ – shekit Aug 13 '18 at 0:03

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