With some devices, the default size of the Serial Buffer used by Ewon may produce unexpected behavior using VCOM functionality.
This KB explains how to change this serial buffer size.
- Ewon Flexy with serial RS232, RS422, RS485 capabilities
IN THIS ARTICLE
To change the serial buffer size, you should modify the parameter VCBUFSIZE that is part of the comcfg1 and the comcfg2 parameters. By default, VCBUFSIZE is equal to 2048. The minimum value you can set is 128 and the maximum 4096.
Since VCBUFSIZE is an advanced parameter, it is not accessible from the VCOM configuration page.
This parameter is only configurable from the tabular edition or through the config.txt file.
Here is an example to change it with Tabular Edition in the Web Interface (Setup > System > Storage > Edit SYSTEM Cfg)
Is search field enter: comcfg1 or comcfg2 depending on which serial port you are using.
Change the value of the VCBUFSIZE and Save.
This was successfully tested on Siemens LOGO or Siemens S5 with value 128.
In comcfg.txt you also have an interesting parameter named "VCOMTempo" that can be helpful to resolve VCOM issues.
This parameter is used to configure the internal frequency/bandwidth method of the VCOM connection.
0 : Disabled (Default)
1: Enable the TCP fragmentation
2: Enable DMA mode (Enabling it might cause reconnection issues. Use it only if you know what you do)
3: Enable both TCP fragmentation and DMA mode