I purchased the new 5" Intelligent display and to my surprise there seems to be an option for TTL or RS232.
I can’t find any documentation in the specs for this option. It looks like you remove R50 to enable RS232. Has anyone tried this? My project uses a remote display and I currently have a small TTL/RS232 board in the display housing to do the conversion. Onboard RS232 would greatly simplify using the Nextion for many of us.
Does anyone have any information on this? I really don’t want to toast my display
If you do not have the serial connected to anything you could measure the voltages on the port with the link connected and disconnected , it appears to be a zero ohms resistor.
Serial TTL, RS232 and RS485 would have been logical options if I was designing such a display.
There is no mention of RS232 in the product overview.
Nor if you scroll down to Interfaces Performance.
Here’s an update on the mysterious RS232 marking on the 5" Intelligent display.
Before doing anything, I measured the open voltage on the RX and TX pins from this display. RX was 3.6V and TX was 4.9V. This surprised me! I’ve always used Enhanced displays in my designs and the Nextion data sheets for these indicate they are compatible with 3.3V logic. Apparently they changed the Intelligent displays to run 5V TTL levels, which means (at least to me) that they are not safe to interface directly to 3.3V CPUs since many are not 5V tolerant on their inputs. My remote display connects to a Teensy 4.1 development board and I use MAX563 dual RS232 IC’s on both ends so I can extend the display away from the CPU. The MAX563 is a 3.3V part and the specs say max input levels are -.3V to VCC-.3V so 5V is not acceptable. It must tolerate the higher voltage because it’s still working but I’m not taking any chances
Next, I removed R50, the 0 ohm resistor shown in the photo and again checked the RX and TX pins on the display. RX was still at 3.6V and TX dropped to 0V. TX should have gone below -3.5V if RS232 was supported. Question answered. I re-installed R50.
In the past I always used 5V to 3.3V level converters to my designs using Nextion displays with 3.3V CPUs. I removed them once I reviewed the Enhanced display specs. Looks like I’ll be adding them back in if I want to use the Intelligent displays.
The UART voltage level of the intelligent displays has been unchanged and documented as being 5V in their respective data sheets since these came to market.
For all the other series, it’s 3.3V.
Understood. This was the first Intelligent display I’ve used. I didn’t think to check the specs, I assumed they would be the same… and we all know what means…
I’m currently using a Teensy 3.2 with a 7" intelligent display and reading through this it seems I should use a level converter, is that correct? Currently the configuration works without one, this is probably because the Teensy 3.2 digital inputs are 5V tolerant.
Nextion datasheet for 7in Intelligent does show 3.3V/5V TTL.
The Teensy 3.2’s digital pins are 5V tolerant (the Teensy LC and 4.x’s are NOT!!!), so, no risk for the Teensy 3.2 on the RX side . On the TX side neither, only in the case that the Teensy 3.2 is close to the lower bound of its specs and the high output level does not reach 3.0V or if there is some attenuation through long wiring. Then, it risks to be too weak to drive the RX input of the intelligent Nextion.
Thanks for the prompt reply. Lucky for me the serial lines are less than 50mm.
Has anyone perhaps used a 74HCT245 level shifter with the nextion?
I would also like to know this question, will there be on-board RS232 in future products, now that I have changed my mind from arduino to STM32, I will use RS232 interface a lot.
I would feel like saving a lot of time if it could be done like this.
Because nextion is cheap, I still want to continue to use it.