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The Modbus Rtu communication protocol is finally available on the distributed line I / O modules Converface. By implementing the Modbus protocol which has now become a de facto communication standard in industrial automation, the Converface modules can now be managed directly by SCADA programs, or be used as remote I / O for PLC devices that implement this communication standard.
The RS485 network connection with only two wires, reduces wiring costs and increases the distance (up to 1,2 Km) between remote devices and the master system, be it PC or PLC.
The Modbus protocol provides a control CRC on the data string and this guarantees high reliability on the communication, avoiding activating logic outputs and / or acquiring the status of logic inputs incorrectly.
The support of Word or Bit management Modbus commands allows to act simultaneously on the whole I / O bank in a single command, or to act on the single I / O point.
The presence of a watch dog inside the module guarantees the reset of the logic outputs in the event of communication failure.
Galvanically isolated I / Os increase the noise immunity of the modules.
The presence of counters up to 100 Hz, allow to perform fast acquisitions on the input signals.
To recognize the modules connected to the RS485 network, the program must be installed on the PC Test of remote serial I / O modules and TCP / IP TRPCOM which can be downloaded from the site.
Select the tab Settings and set the serial port to which the modules are connected, defining the baud rate 9600, protocol modbus RTU.
Select the tab Scan and by pressing the scan button, a scan of all possible modbus addresses from 0x00 to 0xFF will be performed in search of the connected modules. For each module found, the type of module will be indicated.
I can not find the SW Test of remote serial I / O modules e TCP / IP TRPCOM on the download site. I need to configure the 16 Input RS485 acquisition modules. Are there other utilities for managing / displaying these modules?
The TRPCOM program can be downloaded from the Download tab in the page of the site where the product is shown. In reality, the I / O modules distributed on the modbus line do not require any particular configuration. The default module responds to the Rtu modbus commands received from the RS485 serial line. To carry out the communication it is necessary to use a terminal emulation program able to send and receive binary strings, for example the program Toolly. It is necessary to refer to the user manual for the list of managed commands, the serial line must be set to: 9600, n, 8, 1. The default module address (ID) is 01.
For the algorithm of calculation of the CRC it is possible to find in the forum other posts that deal with the topic. Looking at the TRPC26M module, here are some example modbus commands.
To send the command "Read the module's name: ID 46 00 00 (CRC)" it is necessary to send the hex characters $01$46$00$00$E0$0D. The TRPC26M module will respond with the hex characters 01 46 00 00 0C 26 00 DF 05.
To send the input status reading command "Read digital input (Latch) status ID 01 00 SS 00 10 (CRC)" it is necessary to send the hex characters $01$01$00$00$00$10$3D$C6. If all the 16 inputs are not active, the module will respond with the hex characters 01 01 02 FF FF B8 4C. If input D0 is active, the string received will be 01 01 02 FF FE 79 8C, is as follows for the various combinations of active inputs. I also recommend reading this post.
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