I am working with a 800*480 24-bit parallel RGB LCD display. The required clock for the RGB interface has to be between 23 and 27 MHz (typ. 25 MHz).

For testing purposes, I need to display "something" on a large number of displays (e.g. 20), the update rate of "something" not being an issue (it can be a color changing every minute for example). I do not have any piece of information regarding the current sourced/drawn by the interface pins.

The backlight of the display is not an issue here as it can be totally independant from the control interface for each display.

Normally, we are successfully driving one display with a STM32H7 and the suitable LTDC peripheral.

Can I hook up more than one display on the same parallel RGB interface ? The idea here is to test all of the displays (or at least several of them) with only one STM32H7.

My guess is that it should be possible, however at some point the current sourced/drawn by each display on each line, as little as it is, will overcome the current source/draw capabilities of the STM32 (20mA per pin, 140 mA being the maximul output current sourced by sum of all I/Os and control pins). Without the information of the current sourced/drawn by the display I don't know how I can figure out the number of display I can hook up to one STM32.

Another issue I am thinking of and that I cannot evaluate is that by hooking several displays to the same data lines, this will increase capacitance of the line and as a result, rise and fall times of signal might increase to a point where it will no longer be possible to meet proper timing requirements.

Does anybody have any experience in this kind of setup ? There is maybe some kind of dedicated IC for multiplexing that I am not aware of ?

Thank you for your help.

  • \$\begingroup\$ You will definitely need buffers when going beyond a small number. Probably simpler to just use an MCU board for each. Obsolete early prototypes, or builds without the other expensive stuff. \$\endgroup\$ – Chris Stratton Jun 24 at 14:10
  • \$\begingroup\$ Thank you for your answer. I would be already more than happy if I can reduce the number of MCU testing boards from 20 to 10, so 2 displays per MCU. Best would be 3-4 displays per MCU. More might lead to unpactical to handle and too big PCB due to the 40-pin FPC connectors anyway. Would a simple buffer such as 74LCX16244-D (onsemi.com/pub/Collateral/74LCX16244-D.pdf) would do the job for example ? I would place one set of buffers for each display. \$\endgroup\$ – J. K. Jun 24 at 15:49

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