TFP401: HDMI to 18-bit RGB 50-pin FPC screen

Hi there,
some additional informations on the screen to see the feasibility of driving it using a TFP401 board :
1.The resolution is 240x480 and the size is quite small - still possible for the TFP401
2.Typical Clock frequency is 8.57MHz (Min=7.43, Max=11.65MHz)
Looking at this thread
https://e2e.ti.com/support/interface-group/interface/f/interface-forum/902778/tfp401-480-272-support-with-sc7283
it looks like I can downgrade the HDMI clock DCLK to 9MHz (or ~10-11MHz). Is that ok ?
3.What connexion with the 50-pin FPC cable would you recommand ?
Best.

Hi,

The TFP401 can support 18-bit RGB, you would just need to leave the LSB of each color unconnected, but note that this may affect the quality of the image.

Thanks

David

Hi David,

thanks for your prompt reply, some remarks/questions :

- 18-bit RGB : so we can ignore 2 LSB bit on each color
- for HDMI CLK (for instance HDMI of Rpi 3) if we use at 8.5MHz (or even 11MHz) do you confirm this  will work ?
- Concerning the pinout connexion between the TP401 and the screen can you confirm how to wire the different signals ? namely CSX, SDOI, TB_RL, SD, XRES, SCL, PCLK, DE, HS, VS, TLD
For reference the schematic of the Adafruit TP401 HDMI-to-RGB converter board.

Best. Zabieru.

Zabrieu

The max Tpixel is 40ns, which is 25MHz min input clock requirement. So the TFP401 will not able to support 8.5MHz or 11MHz input clock.

Do you have the spec of the screen so I can look up the pin definition and electrical characteristic of  CSX, SDOI, TB_RL, SD, XRES, SCL, PCLK, DE, HS, VS, TLD?

Thanks
David

David,

thanks for your answer and below is an extract of the electrical characteristics for on/off procedure

Also I see a nvidia forum post with a similar frequency conditions screen using a TFP401

post : https://forums.developer.nvidia.com/t/undesired-horizontal-lines-and-broken-pixels-on-the-lcd/195806

screen : http://www.amulettechnologies.com/wp-content/uploads/2019/10/Amulet-Technologies-AM043NBG01.pdf (p10/18)

looking forward to correctly use and connect this screen with the TFP401.

Best.

Hi,

I can't answer any questions on a non-TI forum. But the TFP401 datasheet defines the min clock frequency to be 25MHz and max to be 165MHz. We can not guarantee device operation if the TFP401 is operating outside the recommended operation condition.

Do you have the actual LCD panel spec you can share?

Thanks

David  

Hi David,

thanks for your reply, please find attached the LCD screen specs datasheet for your information.

Thanks.

Zabieru.

KYOCERA_ T-55931GD018HU-T-ANN（55931ANe-_STD）.PDF

Zabieru.

Table 3.3.1 of the LCD module lists the max clock frequency to be 11.65MHz. With TFP401A ODCK minimum clock of 12.5MHz when configured in 2pixel/clk, the TFP401A will not able to support this particular panel.

And looking at Table 5.1 pin assignment, you just need to connect PCLK, HS, VS, and DE to the TFP401A, every other pins can be tied low or high following Table 5.1 recommendation. But again, this LCD module will not able to support TFP401A output clock frequency.

Thanks

David 

David,

thanks for your reply and clarifications

1.electrical connexions
to be exhaustive, pins to connect R, G, B (18-bit), GND, VDD (3V3?), VDDI (3V3?), PCLK, DE, HS, VS?
other to be L or H level on the TFP401A pin board ?

2.Frequency

How do you configure the TFP401A in 2pxl/clk mode ?
Best. Zabieru.

Zabieru

1.electrical connexions
to be exhaustive, pins to connect R, G, B (18-bit), GND, VDD (3V3?), VDDI (3V3?), PCLK, DE, HS, VS?
other to be L or H level on the TFP401A pin board ? 

Correct

2.Frequency

How do you configure the TFP401A in 2pxl/clk mode ? 

This is configured through the PIXS pin as shown below. But in 2pxl/clk mode, we can't support this panel because the frequency is out of spec.

Thanks

David

David,

thanks for your confirmation and I plan to use the Adafruit TFP401A board for a simple test.
This board has the PIXS pin connected to GND which makes PIXS=1pxl/clk
What will happen if I drive the screen in this 1pxl/clk mode ?
Also concerning the frequency, I see some users "overclocking" the scren by sending it 25MHz frequency which also could work by out of spec.

Cheers, Zabieru.

Zabieru

PCLK will double its frequency in 1pxl/clk configuration. I can't comment on what will happen when you overdrive the LCD panel.

Thanks

David