Controlling a TFT-LCD Screen with PortInOut.h

Mbed OS
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Hi everyone

I’m planing to control a TFT-LCD (240x320px) with a Nucleo U575 in parallel interface mode (intel8080).
To do so I think the PortInOut API is the way to go. Unfortunately I don’t really understand the API and it’s documentation. So there are a few questions which maybe one of you can answer :slight_smile:

(API Documentation: PortInOut - API references and tutorials | Mbed OS 6 Documentation)
In the example code the port is defined with “PortIn p(PortA, 0x0000003F);”

  1. What’s the PortA in mbed? Is it the same as the PA-pins on the Nucleo/STM32?
  2. What does the mask(0x0000003F) do? I see that it’s 8 digits for 8pins. What is specified with the number for each pin?
  3. Is it possible to also have a 16pin port or should I better use the BusInOut API in this case?
  4. Did I get it write, that “p.write200)” converts 200 to binary(11001000) and therefore sets pin 0,1,4 high for one cycle?

I hope someone can help me. Thanks in advance!

Matze

1 Like
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Hello,

I do not have personal experiences with any control with this but my understanding of documentation is as follows:

Yes, it is.

This is settings how many pins and which pins you will exactly control on this port. So from my understanding 3f is 0011 1111 that means 6 pins will be used.

Usually one port holds settings for 16 pins (0-15). BusInOut will be slowest than Port Out.

For number 200 you need 8 bits, so you have to set the mask to 0x000000FF and after write the pins 4,6,7 will high until you change them.

BR, Jan

3

Additional hints:

The C++14 standard allows us to use binary literals and digit separator (single quote) so we don’t have to bother with hexadecimal numbers anymore.

For example, to set digits 4, 6, 7 we can write:

port_out.write(0b1101'0000);

or

port_out.write(0b0000'0000'1101'0000);

Please notice also that:

  • We can use arbitrary number of digits.
  • The digit separator can be placed at any position and it can be used in decimal and hexadecimal literals too (for example `PI = 3.141’592’653’589’793 or MEGA = 1’000’000).
1 Like
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Thanks a lot to both of you! this already cleared up many things :slight_smile:
I’ll try to implement the LCD functionality in the next few days. In case of further questions, I’ll come back to you.

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This will work, but its slow. A smarter solution is to use FMC (external Memory) interface. This device needs some setup for the configuration, then for the data transfer you just need to write to a RAM address. This can be combined with DMA and you’ll get pretty fast refresh rates.
A GUI library like lvgl works also very good with this.

6

Hi Jojo
Thanks for the hint. I already checked for the FMC connection. But it semms that mbed doesn’t support that natively, does it?
However if the advantage (refresh rate) is worth it I might be dive deeper into documentations and implement the sources provided by STM…

7

the FMC is very versatile and not very common for other vendors, so it is hard to create a generic OS driver.
But for a display, where you usually want to have a fast refresh, it makes sense to utilize special hardware devices.
Mbed uses the HAL for STM32, so it is easy to use HAL calls in your driver code. I can supply some example for lvgl drivers. I had recently worked on it, but had to pause again. Will send a link later.

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This link might help too.

9

Hi guys

Thanks for your help.
@hudakz : unfortunately I wasn’t able to reproduce your code for my board (Nucleo U575ZI-Q). Even after hours of hardcoding variables and so on.

@JojoS : could you please share your work? I think I only need the setup of the FMC in Mbed. Once I can send data over the interface I will be able to implement all other stuff myself I think. But I’m currently overwhelmed by all HAL-drivers, the nested functions and files, … I’m just losing track :exploding_head:

10

Also I think the Firmware Package for the U5xx isn’t complete yet. What I’m missing really badly are the BSP-libraries as these would make the use of the LCD much easier (in STMCube) I think

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Hello, the porta in mbed should be MCU programming. Porta generally refers to Port A. generally, 8 pins are represented in the single chip microcomputer. Their 0 1 state is controlled and saved by the variable porta (temporarily, because it is generally a macro). Therefore, porta & = 0x04 means porta = porta & 0x04, which is to set all except the third pin to 0 low level, and the third pin remains unchanged.
By the way, one more thing, TFT display is really a very easy to use display!

12

Thanks for the explanation.
I had a look on the link to the TFT displays you provided - I already ordered myself some screens and none of the stone-displays is fitting my needs (2.8" max and sunlight readable/transflective + minimal additional components/pcbs needed as it’s for a mobile application)

Thank you anyways

13

Unfortunately I don’t get the code running.
As this isn’t a problem of Controlling a TFT with mbed but more a migration problem from CubeMX to Mbed (afaik) I just opened another threat on that.

I’d highly appreciate if you could check it out and maybe give me a hint on how to fix it

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