AM437x Display Subsystem

g.f.

Guru 15520 points

Other Parts Discussed in Thread: DS90C363B

Hi,

I have questions about AM437x Display Subsystem(DSS).

My customer are planning to connect LCD to AM437x via DSS.

Their LCD spec is 18bit and LVDS I/F.

DSS are supporting RGB 18bits so that they are thinking to use TTL to LVDS converter.

Q1. On AM437x EVM, DSS are connected to LCD by RGB 24bits. I think Linux SDK are providing LCD driver for AM437x.

Can the customer use this LCD driver as reference? Or do they need to make the LCD driver by themselves for their LCD with no reference?

Q2. My customer also planning to connect LCD to AM335x which have LCD controller.

And they are thinking of using same circuit as AM437x(connection between AM437x DSS and LCD).

AM335x LCD Controller and AM437x DSS are different so I guess they can not use same circuit and need to make circuit for each device, am I correct?

best regards,

g.f.

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi g.f,

While the AM437X DSS supports 18-bit parallel output, the AM335X LCDC does not. To connect an 18-bit display to AM335X normally the LCDC is configured in 24-bit format and the highest 6 bits of each color are connected to the LCD. This however may present problems when using a TTL to LVDS converter. Here is a good material on LCD connectivity: http://processors.wiki.ti.com/index.php/LCD_connectivity It's a bit old, but general rules are valid. On your questions:

Q1. Yes, they can use the SDK display driver. Here is a link to the wiki guide: http://processors.wiki.ti.com/index.php/Linux_Core_DSS_User's_Guide

Q2. See my explanations above about AM335X display formats. Here is a link to the wiki guide: http://processors.wiki.ti.com/index.php/Linux_Core_LCD_Controller_User_Guide You also need to check AM335X Errata Usage Note 3.1.1 for correct connections.

0 g.f. over 9 years ago in reply to Biser Gatchev-XID

Guru 15520 points

Hi Biser,

Thank you for the reply.

I uderstood that same circuit of LCD I/F can't be used between AM437x and AM335x.

I have a question about AM335x LCDC and 18bit LCD Display connection 
to make me sure.

I understand that 24bit mode can be used to connect 18bit LCD Display.
I checked errata sheet of AM335x ("3.1.1 LCD: Color Assignments of LCD_DATA Terminals").
My customer are going to use LCD display which have LVDS I/F, so they are also going to use
TTL->LVDS converter(ex. TI DS90C363B).
http://www.tij.co.jp/jp/lit/ds/symlink/ds90c363b.pdf
In such case, what is the correct connection between AM335x LCDC I/F and DS90C363B?
I attached the block diagram of the connection(only LCD data terminal). 
Can you please take a look and give me an advise?

best regards,
g.f.

AM335x_18bit LVDS LCD Display connection.pdf

0 Biser Gatchev-XID over 9 years ago in reply to g.f.

TI__Guru**** 393215 points

Yes, these are the LCD pins that should be used, but you have got colors wrong. Red and blue must be swapped. See AM335X Errata Rev. F Usage Note 3.1.1, Figure 2 for correct color assignment. Attention must be also given to LVDS transmitter connections. Signals should be connected in such way, that they match the display requirements for RGB/sync data sequencing.

0 g.f. over 9 years ago in reply to Biser Gatchev-XID

Guru 15520 points

Hi Biser,

Thank you for the reply.

Sorry, red and blue connection was wrong.
I modified the block diagram. I'm very sorry, but can you please check again?

best regards,
g.f.

Modified_AM335x_18bit LVDS LCD Display connection.pdf

0 Biser Gatchev-XID over 9 years ago in reply to g.f.

TI__Guru**** 393215 points

Yes, this is OK now. The H/V sync signals, DE and pixel clock should also be connected, but they have dedicated pins. One additional consideration - note that DS90C363B has a max. pixel clock frequency of 65MHz. You should check whether that's enough for your display requirements.

0 g.f. over 9 years ago in reply to Biser Gatchev-XID

Guru 15520 points

Hi Biser,

Thank you so much. I understood.
The clock requirement is 45MHz so DS90C363B is fine. Thank you.

best regards,
g.f.

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AM437x Display Subsystem