--- title: "UART pin voltage" url: "https://maker.wiznet.io/forum/11217" markdown_url: "https://maker.wiznet.io/forum/11217/md" type: "Forum topic" category: "Wireless" author: "soellicha" created: "2015-08-07T17:30:33+09:00" last_activity: "2017-05-04T08:36:36+09:00" language: "en" views: 741 replies: 7 source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)" --- # UART pin voltage ## Question Asked by soellicha on 2015-08-07 in Wireless. Hello, I am going to connect the Wizfi250 board to an MCU PIC 18F877A. 1 . Are the UART pins of Wizfi250 5v or 3.3v compatible? Can I connect directly the MCU to the Wzfi250 or should I have resistors as well? 2 . What about the CTS and RTS pins on the wizfi250? Should I leave them unconnected or short them? 3 . If I send data from UART or SPI what would be the form? String of data ( IN THE FORM OF “AT”) ? Thank you, Best Regards, Andreas Achilleos ## Replies ### Reply 1 by kaizen, 2015-08-09 Hi These are my answer. 1 . Are the UART pins of Wizfi250 5v or 3.3v compatible? Can I connect directly the MCU to the Wzfi250 or should I have resistors as well? > No It’s not compatible. UART pins of WizFi250 can be used for 3.3V. If you want use 5V with your MCU, I think you need to use Voltage-Level Translator as TXS0104EPWR. 2 . What about the CTS and RTS pins on the wizfi250? Should I leave them unconnected or short them? > Yes, you can disconnect CTS and RTS pins on the WizFi250 if you don’t need high speed performance during serial communication which more than 230400 baud-rate. 3 . If I send data from UART or SPI what would be the form? String of data ( IN THE FORM OF “AT”) ? > You can use string data when WizFi250 send data to peer device. For more detailed information about method for sending data, refer to this document. > ### Reply 2 by soellicha, 2015-08-10 Hello Kaizen, I appreciate your response. 1 . Instead of using a Voltage-Level Translator as you said can I just use resistors to do that?![](https://maker.wiznet.io/forum_uploads/wiznet/original/1X/46ced4dd68d3a65e8e047cfe5954dbe1e7783e45.png) 2 . Can I first configure wizfi250 as TCP server/AP from the web page configuration and then transfer data with peer system? If yes what would be the command sequence? Is this the command mode? For example: 1.Go to S2W setting on the wizfi250 browser- configure it as TCP server 2.send from MCU through UART the command AT+SSEND 3.Receive OK from wizfi250. Or I should use the following commands: 1.AT+SCON 2.AT+SMGMT 3.AT+SSEND 4.AT+SFORM with that specific order? Thank you, Best Regards, Andreas Achilleos ### Reply 3 by felix, 2015-08-11 Hello Andreas, ![](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/48.png) soellicha: > 1 . Instead of using a Voltage-Level Translator as you said can I just use resistors to do that? This setup will not work. You have to switch both resistors, the 1k needs to be connected to +5V and the 2k resistor needs to be connected to GND. The corresponding equation for calculating the voltage divider does normally not show the output voltage but the voltage that drops over the appropriate resistor. Best regards, Felix ### Reply 4 by soellicha, 2015-08-12 Thank you Felix, I will try that! ### Reply 5 by soellicha, 2015-08-12 Hello, While I am sending data from the android app to the wizfi I do not see the Tx/Rx leds blink! Is that normal? Thank you ### Reply 6 by wizdaniel, 2015-08-13 Hi soellicha, No. It’s not normal. When you send data, you can see the Tx/Rx led’s blink. Please check the IP address at Smartphone. Is that correct IP? [quote] There are simple AT command for setting up the AP mode. [url][http://wizwiki.net/wiki/doku.php?id=products:wizfi250:wizfi250pg:start\[/url\]](http://wizwiki.net/wiki/doku.php?id=products:wizfi250:wizfi250pg:start%5B/url%5D) at+wset=1,WizFi250AP at+wsec=1,WPA2,12345678 at+wnet=0,192.168.11.1,255.255.255.0,192.168.11.1 at+wjoin at+scon=o,tsn,5000,1[/quote] Otherwise, I recommend using other TCP Client Application in play store. Thanks. ### Reply 7 by soellicha, 2015-08-13 Hello wizdaniel, Thank you for your reply, Even if the Tx led is not blinking, I still manage to send data from android app to the Wizfi and then to the MCU through UART. I have not though , managed to transfer data from MCU to WIzfi. Once the leds tried to blink when I raised the Rx pin of wizfi250 up to 5V! Thank you, Best Regards --- Source: https://maker.wiznet.io/forum/11217