# WIKI : Sample apps with Modbus protocol over serial port **URL:** \ **Category:** Uncategorized\ **Created:** [July 5, 2018, 1:53pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670 "2018-07-05T13:53:23Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Francis.duhaut](https://sea2.discourse-cdn.com/flex016/user_avatar/mangoh.discourse.group/francis.duhaut/32/350_2.png) [@Francis.duhaut](https://mangoh.discourse.group/u/Francis.duhaut)\ **Post date:** [July 5, 2018, 1:53pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/1 "2018-07-05T13:53:23Z")
Hello all, Just a message to share with you small application who use a FDTI USB serial port and modbus protocole. This is a good base if you want to implement data access with serial port over modbus protocol. Only function 3 and 16 are implemented with CRC calculation but it’s easy to add more. I use le\_fdMonitor\_Create() to pollin into a handler incomming modbus messages. Apps use a circular buffer to “eject” bad data and read only a good modbus frame. You will find example to read/write data to a C Struct over modbus. This was tested with MAngoh red and WP76 / R9 and legato 18.05. Driver for FDTI USB serial port is loaded at apps startup. [wiiq3Monitor.zip](https://mangoh.discourse.group/uploads/short-url/oOkjdIVogR4eCziWAkkXSkDrt5r.zip) (162.9 KB) Example : connect a USB FDTI serial converter to main USB connector start apps open a terminal at 115200bps (I use Hercules terminal for ex) send this modbus frame : {01}{03}{12}{4D}{00}{10}{D1}{69} -\> Slave address = 0x01 function 0x03 address 0x124D and read 16 registers (0x0010) CRC frame is 0xD169 -\> check the answer {01}{03}{20}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{00}{92}{7A} -\> 0x01 slave address -\> 0x03 function 0x03 -\> 0x20 is 16 registers of 2 bytes = 32 bytes -\> after is data mapped to the CStruct at 0x124D -\> 0x927A is the CRC ![image](https://us1.discourse-cdn.com/flex016/uploads/mangoh/original/1X/1959a538459b703eab562cb07a399417d97a6766.png) Have a nice day. Francis. ---
**Author:** ![Madan](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Madan](https://mangoh.discourse.group/u/Madan)\ **Post date:** [August 9, 2018, 5:51pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/2 "2018-08-09T17:51:08Z")
Hi Probably this is the only example out there on Legato for serial port communications. I have used this code for basic serial port communication. Picked serial.c/.h and relevant configurations. Built and uploaded the code in to mangOH Red. Application exits because it could not find comport. (error no 2). I have added the /dev/ttyHS0 and /dev/ttyHSL1 for R/W. But open port fails always. Tested on both ports. Both ports are available in /dev folder. If the ports are already in use, I think the error no. should have been something like ‘access denied’. Actual plan is to use the console USB to push data into PC (testing phase only) Is there anything I am missing? Thanks ---
**Author:** ![Francis.duhaut](https://sea2.discourse-cdn.com/flex016/user_avatar/mangoh.discourse.group/francis.duhaut/32/350_2.png) [@Francis.duhaut](https://mangoh.discourse.group/u/Francis.duhaut)\ **Post date:** [August 9, 2018, 6:40pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/3 "2018-08-09T18:40:59Z")
Can try with unsandboxed apps? I use Ftdi usb serial converter without any issue. My apps are unsandboxed. Francis ---
**Author:** ![Madan](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Madan](https://mangoh.discourse.group/u/Madan)\ **Post date:** [August 10, 2018, 5:30am UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/4 "2018-08-10T05:30:25Z")
Thank you Francis. I will try unsandboxing. ---
**Author:** ![Madan](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Madan](https://mangoh.discourse.group/u/Madan)\ **Post date:** [August 10, 2018, 12:13pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/5 "2018-08-10T12:13:29Z")
Unsandboxing did the trick. It works now and I am able to get the Apps serial out on the console port. Thanks Francis. ---
**Author:** ![mpetersen](https://sea2.discourse-cdn.com/flex016/user_avatar/mangoh.discourse.group/mpetersen/32/1177_2.png) [@mpetersen](https://mangoh.discourse.group/u/mpetersen)\ **Post date:** [August 21, 2020, 6:50pm UTC](https://mangoh.discourse.group/t/wiki-sample-apps-with-modbus-protocol-over-serial-port/1670/6 "2020-08-21T18:50:39Z")
Any updates you can share on your Modbus implementation? …would be most appreciated! Thanks