Teensy 3.2 with multiple serial displays

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Raymond_B

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I did some searching, but I am still a little unclear.

I have recently built a project that runs a single Nextion display over a serial conenction on my Teensy 3.2. All the Nextion discussion aside, what would be the overhead on the Teensy be when running 2 or even 3 serial displays?
 
It really depends on how much processing needs to be done on the Teensy to support a display. If the display is dumb, and the teensy has do the full rendering locally and send out bits to redraw the entire screen, than adding a display essentially doubles the work load. If on the other hand, the display has its own microprocessor on the display, and you are sending high level commands (print text, draw box, etc.) then the overhead is much less, and it depends on what you need to do in your program.

Note, the Teensy only has 3 serial lines, so in general you would only be able to add 3 displays. Depending on how much I/O you are going to do, you might be able to add a 4th with AltSoftSerial that does all of the processing in software.
 
Very little overhead, you send only high level commands to it. In addition, the serial speed of the nextion is quite slow..
 
Quick read of spec sheet - I saw only UART serial at up to 115200 baud. For a nice, fancy graphics display with touch screen this seems to be a rather low speed interface. And there's an SD card socket and FATFS onboard.
Or did I miss something? Seems like a display of this class should have at least I2c or better, SPI.

Indeed, the question is how much screen data are you going to be sending at 115200, and are you using the touch screen - which may be trying to send data at the same time the screen is being updated (doable). And we assume that the Nextion processor itself does most of the compute-intensive work, e.g., math for drawing curves, etc.

Using DMA to send gobs of data to the display via UART would help if the Teensy is over-worked.

Perhaps their strategy is to pre-compile GUI content on the PC, put on flash card, then the serial port is used to send metadata such as "display form #123" and "here is text to plug into widgets".
So the serial interface doesn't (can't ?) send bitmaps or some graphics rendering language instructions.
 
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almost.
they store the widgets on a on-board flash chip. and it takes ages to upload... and the editor is -sorry- crap.
the serial speed is ok for commands like "display widget".

But not for more dynamic content.
 
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