Hi guys,

Been studying how to interface my ARM LPC1768 mcu with a 3.5 inch TFT LCD. I've been searching the info on the internet. There's this digital data input (for RGB) which is around 18 (3x6) or 24 (3x8) pins on the LCD. I've been referencing other people's design from the internet and found out that some of them just connect these digital data input pins to the ground. But some people connect these pins to LPC1768 GPIO. Do you guys know why?

 

I've been referencing other people's design from the internet and found out that some of them just connect these digital data input pins to the ground. But some people connect these pins to LPC1768 GPIO. Do you guys know why?

Its depends on the software used i.e.. the protocol to communicate with the LCD ,in some design we don't need some of the pins ,we normally ground it or pull it up i.e.. connect it to positive rail (logic high), for example in 3310 LCD which use a PCD8544 as driver have a reset pin which should be controlled by software for proper initialization ,but in prototype design, while I am testing code I pull up that pin i.e.. I connect that pin to logic high (positive rail), as in PCD8544 reset pin is active low.

Another reason for grounding any digital input pin, in digital circuits is .In genneral if you keep a digital input pin floating it could give out an undefined logic at its output and it cause many problem in different applications, so it is a good practice whenever any digital input is not used just ground it.

Good Luck

 

The design that I found from the internet connect all the LCD RGB data pins to the ground. Seems like it only connect SDI, SDO, SCLK and CS pins to the mcu. Does this means if the LCD got SPI interface, the RGB data pins can be connected to the ground?

 

What is the part number of your LCD?

hgmjr

 

What is the part number of your LCD?

hgmjr

I've attached two schematics from two design I found on the internet. Both also connects the LCD RGB data pins to the ground.

 

You have to provide us the number of your controller chip of your LCD, every LCD have a controller chip with which your mcu communicates. Now in the schematics you provided, their is no information of your LCD controller chip, its just the connectors, but by looking at the connectors pin names it seems your LCD could communicate in different modes like parallel and serial, and the serial one is used like SDO,SDI,SCL and the parallel pins are not used so they are grounded. To know more you have to give us the number of your controller/driver chip for your LCD.

And yes the LCD got SPI interface as its commutating in serial way ,at least what it shows in the schematics

Good Luck

 

You have to provide us the number of your controller chip of your LCD, every LCD have a controller chip with which your mcu communicates. Now in the schematics you provided, their is no information of your LCD controller chip, its just the connectors, but by looking at the connectors pin names it seems your LCD could communicate in different modes like parallel and serial, and the serial one is used like SDO,SDI,SCL and the parallel pins are not used so they are grounded. To know more you have to give us the number of your controller/driver chip for your LCD.

And yes the LCD got SPI interface as its commutating in serial way ,at least what it shows in the schematics

Good Luck

I do not have the LCD driver chip part number. I found all this schematics in the internet.

 

Then what's the point?
How you are going to communicate with your LCD,without knowing the protocol you can't do it...

 

The design that I found from the internet connect all the LCD RGB data pins to the ground. Seems like it only connect SDI, SDO, SCLK and CS pins to the mcu. Does this means if the LCD got SPI interface, the RGB data pins can be connected to the ground?

I've seen it done that way on the display I use. Of course, serial data is not as fast as a parallel data load but quite serviceable in many situations. For parallel data mine has the option of a word size of 18, 16, 9, or 8 bits wide.

Unused lines would of course be grounded.