USB-UART CP2102 TXD voltage compatibility with 3.3V ATmega328 input

TECHNICAL SUPPORT NULA Development Boards
1

Customer:

I have a question about the USB-UART module. According to your schematic, TXD is directly connected to the microprocessor (Arduino AT328) input. The CP2102 datasheet specifies a maximum allowed voltage on input pins of 5.2V, but does not define the maximum output voltage from TXD. If that voltage is 5V, could it damage the RX input on the microprocessor when running at 3.3V? Or does the ATmega328 tolerate this?

Second question (I haven’t tested it): can both FTDI and CP2102 drivers be active on the same PC simultaneously? One for example on COM5 and another on COM6? They probably both need to be the same type.

Original message (Croatian)

Imam jos jedno pitanje.

Nejasnoca sa vasim modulom usb-uart. Prema vasoj shemi txd se izrazno vodi na ulaz mikroprocesora (arduino at328). Preme datasheet za cp2102 definiran je maksimalni dozvoljeni napon na ulazne pinove od 5.2v ali nigdje nije definira maksimalni izlazni napon od txd. Ako je taj napon 5v, dali moze ostetiti ulaz u mikroprocesor rx kada on radi na 3.3v. Ili atmega328 to tolerira.

Drugo pitanje (nisam isprobao) da li u istom pc mogu biti aktivna oba drivera fdti i cp2102. Jedan za na primjer comport5 a drugi comport6 ?. Vjerojatno oba moraju biti istog tipa.

Unapred zahvaljujem

Originally submitted via email support on 13 February 2018. Migrated to the forum for community visibility.

2

Customer:

Another question: in your KKM Bluetooth documentation, do you have a connection schematic for Bluetooth to Croduino Nova? From what I understand, Nova disconnects from USB and receives external power. Bluetooth connects to pins 0,1 RX,TX on Nova. The issue is: even when the USB connector is disconnected, the internal USB-UART adapter remains active and sends a LOW idle signal on the processor’s RX. If we connect Bluetooth TX to Nova RX, these two signals conflict. Is this a problem?

Original message (Croatian)

Jos jedno pitanje

U vasem KKM Bluetooth dali ste shemu spajanja bluetooth na Novu. Kako razabirem Nova se odspoji od USBa i dade se vanjsko napajanje. Bloetooth se spoji na pinove 0,1 Rx,Tx Nove. Dilema je, makar se odspoji Usb prikljucak, interni adapter Usb-Uart je ziv i daje signal mirovanja LOW na Rx procesora. Ako spojimo Tx Bluetootha na Rx Nove, ta se dva signala sudaraju. Problem?

3

Soldered Support:

You are correct. You need to use the Software Serial library, which simulates serial ports (UART) on any other pins.

https://www.arduino.cc/en/Reference/SoftwareSerial