I worked out some of the connections between Metro and RA8875, but only MISO, MOSI, Clock, are obvious.
Chip Select, Wait, Interrupt, and others are not obvious and I would like a little guidance so as to get it right the first time.
My diagram is attached.
Thanks
Metro M4 connect RA8875 connect 5" TFT without Touchscreen
Moderators: adafruit_support_bill, adafruit
Please be positive and constructive with your questions and comments.
- StanHemphill
- Posts: 7
- Joined: Wed Apr 14, 2021 9:00 am
- adafruit_support_mike
- Posts: 67446
- Joined: Thu Feb 11, 2010 2:51 pm
Re: Metro M4 connect RA8875 connect 5" TFT without Touchscre
The Reset pin is an input for both devices, so you don't want to connect them.
Use one of the Metro's GPIO pins to control the RA8875's Reset pin. The microcontroller will toggle that pin when it first connects to the RA8875 to dump any unwanted data and put the device in a known state.
The Vin pin provides power for the whole breakout. The board has a built-in 3.3V regulator, and the output from that regulator is connected to the 3Vo pin.. adding the extra characters for 3.3V would make the silkscreen marking invconveniently large. You can connect 5V to the Vin pin and draw 3.3V from the 3Vo pin, or you can leave Vin unconnected and power the breakout from a 3.3V power source connected to 3Vo.
The Lite pin controls the display's backlight. Connect that to another GPIO pin if you want to control the screen's brightness.
Chip Select is a mandatory signal used in SPI. A peripheral device's CS pin has to be low before it will listen to signals on MOSI and SCK. Again, connect that to one of the Metro's GPIO pins.
The INT and WAIT signals are messages from the RA8875 to the microcontroller. INT tells the microcontroller the RA8875 wants its attention for something, and WAIT tells the microcontroller that the RA8875 needs more time to process the last command it was given. Once again, those connect to GPIO pins.
The code that controls the RA8875 will want to know which GPIO pins all those signals are connected to.
Use one of the Metro's GPIO pins to control the RA8875's Reset pin. The microcontroller will toggle that pin when it first connects to the RA8875 to dump any unwanted data and put the device in a known state.
The Vin pin provides power for the whole breakout. The board has a built-in 3.3V regulator, and the output from that regulator is connected to the 3Vo pin.. adding the extra characters for 3.3V would make the silkscreen marking invconveniently large. You can connect 5V to the Vin pin and draw 3.3V from the 3Vo pin, or you can leave Vin unconnected and power the breakout from a 3.3V power source connected to 3Vo.
The Lite pin controls the display's backlight. Connect that to another GPIO pin if you want to control the screen's brightness.
Chip Select is a mandatory signal used in SPI. A peripheral device's CS pin has to be low before it will listen to signals on MOSI and SCK. Again, connect that to one of the Metro's GPIO pins.
The INT and WAIT signals are messages from the RA8875 to the microcontroller. INT tells the microcontroller the RA8875 wants its attention for something, and WAIT tells the microcontroller that the RA8875 needs more time to process the last command it was given. Once again, those connect to GPIO pins.
The code that controls the RA8875 will want to know which GPIO pins all those signals are connected to.
- StanHemphill
- Posts: 7
- Joined: Wed Apr 14, 2021 9:00 am
Re: Metro M4 connect RA8875 connect 5" TFT without Touchscre
Connecting a 3V3 source to the 3Vo pin would be connecting a voltage source to the output of the internal regulator, yes? Seems a 5V0 supply at Vin and let the electronics do it’s job is better.
I understand that apart from MISO and MOSI that everything else goes to a pio. Surely there is a default of most frequently used assignment for the pios. The *.h libraries would have been developed assuming something?
Sincerely,
Stan
I understand that apart from MISO and MOSI that everything else goes to a pio. Surely there is a default of most frequently used assignment for the pios. The *.h libraries would have been developed assuming something?
Sincerely,
Stan
- adafruit_support_mike
- Posts: 67446
- Joined: Thu Feb 11, 2010 2:51 pm
Re: Metro M4 connect RA8875 connect 5" TFT without Touchscre
Yes, but a voltage regulator with nothing connected to its upstream supply pin is basically a reverse-biased diode. It doesn't interact with the rest of the circuit.StanHemphill wrote:Connecting a 3V3 source to the 3Vo pin would be connecting a voltage source to the output of the internal regulator, yes?
Any time our libraries assume a default pin, the example sketches will have a comment identifying it. You can also check the tutorial linked from the product page.StanHemphill wrote:I understand that apart from MISO and MOSI that everything else goes to a pio. Surely there is a default of most frequently used assignment for the pios. The *.h libraries would have been developed assuming something?
Functionally, it doesn't matter much for pins configured as outputs. The input pin connected to the INT signal should be able to handle interrupts, and any other requirements should also be described in the example sketches.
- StanHemphill
- Posts: 7
- Joined: Wed Apr 14, 2021 9:00 am
Re: Metro M4 connect RA8875 connect 5" TFT without Touchscre
OK, got it, thanks a million.
Stan
Stan
- StanHemphill
- Posts: 7
- Joined: Wed Apr 14, 2021 9:00 am
Re: Metro M4 connect RA8875 connect 5" TFT without Touchscre
Hi Mike,
I wrote my inquiry in a word file saved to PDF. I needed a lot more editing tools and pix insertions than this window allows.
Sincerely,
Stan Hemphill
I wrote my inquiry in a word file saved to PDF. I needed a lot more editing tools and pix insertions than this window allows.
Sincerely,
Stan Hemphill
Please be positive and constructive with your questions and comments.