# Nano 4 Docs inconsistent, there are two Serial instances supported **URL:** \ **Category:** Nano R4\ **Created:** [November 15, 2025, 1:55pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454 "2025-11-15T13:55:01Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![camsysca](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/camsysca/32/1015228_2.png) [@camsysca](https://forum.arduino.cc/u/camsysca)\ **Post date:** [November 15, 2025, 1:55pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/1 "2025-11-15T13:55:01Z")
Start here: [https://docs.arduino.cc/hardware/nano-r4/](https://docs.arduino.cc/hardware/nano-r4/) First, let’s check the tech-specs part of that page: [https://docs.arduino.cc/hardware/nano-r4/#tech-specs](https://docs.arduino.cc/hardware/nano-r4/#tech-specs) UART - 1… Next, let’s go to page 4 of the handy “datasheet” [https://docs.arduino.cc/resources/datasheets/ABX00142-datasheet.pdf](https://docs.arduino.cc/resources/datasheets/ABX00142-datasheet.pdf) Note, in Section 2.1, the table of features itemizes “Communication UART (1x)” (By the way, despite internal references in section 2.8 claiming the info is presented, I could find no indication in this document detailing what pin the RGB LED is on. Another minor deficit, might need raising as a separate post). Next, go here: [https://docs.arduino.cc/tutorials/nano-r4/user-manual/](https://docs.arduino.cc/tutorials/nano-r4/user-manual/) scroll down to the multicolour pinout depiction. UART1 is depicted, but no reference for the UART associated with the USB connection… Next, on the schematic: > **[ABX00142-schematics.pdf](https://docs.arduino.cc/resources/schematics/ABX00142-schematics.pdf)** you’ll find reference to TXD and RXD, and USB\_D\_N and USB\_D\_P… Next, go back to the user manual for a minute, scroll further to the Digital Pins description, and you’ll find reference to D0 and D1, as “UART” RX and TX ( **NOT** UART1)… Scroll down to the section on UART communication, and you’ll get a full description of the usage of the TWO UARTs in the device. That’s as far as I’ve dug, so far. So, yes, I do realize that there are TWO UARTs in play, and that one is dedicated to the USB interface while the other is for the user to use, which sort of clouds the issue, but there are TWO functional UARTs, no question. I would suggest that the documentation is extremely inconsistent if not downright misleading in this regard, leaving anyone with Nano experience(including me) with the impression that there is still only 1 UART, with it’s dual purposes, on the basis of the tables referenced above. It was only when I dug deeper that I found a Serial/Serial1 reference. A pity, as I’m well on the way to an ATMEGA328PB solution to effect the same upgrade(two UARTs) on my current project; buying several R4s would have been a worthy alternative, saving me time, money, and irritation. ---
**Author:** ![UKHeliBob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ukhelibob/32/215663_2.png) [@UKHeliBob](https://forum.arduino.cc/u/UKHeliBob)\ **Post date:** [November 15, 2025, 2:06pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/2 "2025-11-15T14:06:49Z")
> [@camsysca](#): > > It was only when I dug deeper that I found a Serial/Serial1 reference. The "cheat sheet" [https://docs.arduino.cc/tutorials/uno-r4-wifi/cheat-sheet/](https://docs.arduino.cc/tutorials/uno-r4-wifi/cheat-sheet/) seems clear as to the two serial ports, the pins used and the serial port names ---
**Author:** ![camsysca](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/camsysca/32/1015228_2.png) [@camsysca](https://forum.arduino.cc/u/camsysca)\ **Post date:** [November 15, 2025, 2:57pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/3 "2025-11-15T14:57:46Z")
Why would one necessarily go to Tutorials for a cheat sheet to find out about a product’s features? Sure, it’s one path to the answer, but? You may close this thread if you wish, particularly if that’s the official doctrine. ---
**Author:** ![UKHeliBob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ukhelibob/32/215663_2.png) [@UKHeliBob](https://forum.arduino.cc/u/UKHeliBob)\ **Post date:** [November 15, 2025, 3:05pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/4 "2025-11-15T15:05:54Z")
I am not suggesting that the documentation that you found is not confusing or incomplete However, it does not seem unreasonable to look look at a tutorial to find out about the features of a product Note too that there is nothing official about what I said. I am not employed by Arduino or paid by them in any way ---
**Author:** ![camsysca](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/camsysca/32/1015228_2.png) [@camsysca](https://forum.arduino.cc/u/camsysca)\ **Post date:** [November 15, 2025, 3:15pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/5 "2025-11-15T15:15:54Z")
> [@UKHeliBob](#): > > does not seem unreasonable to look look at a tutorial Sure. It also doesn’t seem unreasonable to look at the documents I cited. I wouldn’t look for a “tutorial” about a specific product’s salient features, because to me, a '“tutorial” is about how to do something, not what features it has. The latter is contained in a tech-spec, but wouldn’t be something a single tutorial would list. ---
**Author:** ![MicroBahner](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/microbahner/32/238923_2.png) [@MicroBahner](https://forum.arduino.cc/u/MicroBahner)\ **Post date:** [November 15, 2025, 3:18pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/6 "2025-11-15T15:18:25Z")
> [@camsysca](#): > > So, yes, I do realize that there are TWO UARTs in play, and that one is dedicated to the USB interface while the other is for the user to use, No, there are not two UARTs in play. There are two serial interfaces in play, one native USB at USB-C and one UART at D0,D1. USB is a very different serial interface compared to UART, even if it can be used ( via Serial() ) just like an UART interface. > [@camsysca](#): > > Scroll down to the section on UART communication, and you’ll get a full description of the usage of the TWO UARTs in the device. Ok, they write about 2 UART, but that's obviously wrong. Despite the fact, that both can be used very similar via Serial, there are not two UART interfaces. ---
**Author:** ![camsysca](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/camsysca/32/1015228_2.png) [@camsysca](https://forum.arduino.cc/u/camsysca)\ **Post date:** [November 15, 2025, 3:27pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/7 "2025-11-15T15:27:59Z")
You are correct: > **[RA4M1.pdf](https://elecohm.com/wp-content/uploads/2024/09/RA4M1.pdf)** > > 5.92 MB So then, while there is still an inconsistency, the nature of the issue is different. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [May 14, 2026, 3:28pm UTC](https://forum.arduino.cc/t/nano-4-docs-inconsistent-there-are-two-serial-instances-supported/1414454/8 "2026-05-14T15:28:26Z")
Closed on May 14, 2026, 3:28pm UTC This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.