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Cannot connect to the PLC device error in the PLC Control Panel

Last Updated: December 05, 2011

What should I check for when the PLC Control Panel cannot connect to the PLC device?


Check for the following when this error is displayed by the Control Panel

  •       Is any other Cypress software running that has connected to the USBI2C bridge? The USBI2C Bridge can only be connected to using one program at a time. Examples of other software that uses the bridge are PSoC Programmer and Bridge Control Panel. Close all the open Cypress programs and restart the PLC Control Panel.
  •       Is the USBI2C bridge connect to the PC and does it appear in the USB-I2C bridges section of the Control Panel as shown below. If it does not appear please uninstall and reinstall the latest build of PSoC Programmer and restart the PLC Control Panel application. A green LED should power on the USBI2C bridge once it is successfully connected to the PC.

  • Is the bridge connected to the I2C header of the board? For the CY3272, the I2C header is J5. For the CY3273, the I2C header is J8. For the CY3274 and CY3275, the I2C header is J15. A picture showing the correct connection is shown below for the CY3273 kit. It is similar for all the other kits.
  • Is the correct I2C bridge selected? If you have two bridges connected to the PC as shown below, choose the one that is connected to the board you are trying to connect to. Use the Blink GRN LED button to blink the led on the USBI2C bridge that is currently selected.


  • Is the correct I2C slave address selected? For the CY3272/3, the I2C address can be configured by the I2C DIP (S1) switch on the board. When this switch is in the off position, the I2C address is 0x01 and when it is on, the I2C address is 0x7A. For the CY3274/5, the USB-I2C bridge can only connect to FSK Modem + Network Modem + I2C Bridge option of the PLT User Module. The I2C slave address is a configurable property of the User Module. The user module property value is in decimal form, while the Control Panel GUI I2C address is in hexadecimal form. For example if the user module I2C Slave Address property is set to 15, the Control Panel should connect to the PLC Address “0f” by selecting the “Other” option.
  • If the “USBI2C options” is set to “+5V PWR”, make sure a jumper is placed on the USBI2C bridge at the J1 position and make sure there is no jumper on the PWR jumper header of the PLC board. When the connect button is clicked, a red LED on the USBI2C bridge should turn on. If it is set to “EXT. PWR” place a jumper on the PWR jumper header of the PLC board. The red LED on the USBI2C bridge should begin to blink.

          Note that the USBI2C bridge can connect with any I2C Clock Rate.

  • If the connection is successful, the GUI should display a PLC #0 Connected in the status bar as shown in the picture below.


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