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Information in this article applies to:

  • C51 Version 7.00
  • µVision Version 2.30
  • Cypress EZ-USB FX Family Development Board
  • Cypress EZ-USB FX2 Family Development Board


I am using the Cypress EZ-USB FX2 Development Board and the Keil 4K evaluation compiler with the default Keil monitor for the Cypress FX SIO-1. I have configured the Keil debugger to MON51, COM1, 38400 baud, and serial interrupt to halt the program. I cannot get the monitor to connect. I only receive the following error message:

Can Not Connect

What am I doing wrong?


The EZ-USB board and the Keil tools should connect immediately with no problems. When problems do crop-up they are usually easy to solve. Following is a list of items to check to insure that you have the tools and board properly configured.

  1. Make sure you have selected the correct COM port in the Keil Monitor 51 debugger settings.
  2. Check to be sure that the serial cable is connected to the correct COM port on your PC and to the correct port on the EZ-USB board. For example, if you use the default monitor which uses SIO-1 on the EZ-USB board, you must connect the serial cable to the SIO-1 port on the development board.
  3. Be sure that USB cable is connected between the PC and the EZ-USB board. You may use the EZ-USB Control Panel to verify that the board is connected to the PC.
  4. Make sure that the EZ-USB Monitor is downloaded to the board. Using the USB Control Panel, select the Get Device ICON and make sure that your board enumerates with a Vendor Identification (VID) = 0x0547 and Product Identification (PID) = 0x0080. This allows the monitor to be downloaded via the ezmon.sys driver.
  5. Check to see that the D3 (or D7 for the FX2) LED on the board is green. This LED indicates that the monitor has been downloaded successfully. If the LED is not green, press the FX2 RESET button and the green LED should turn on. If not, in the EZ-USB Control Panel, click the LoadMon button to load MON51. After loading, the green LED should be on.
  6. Verify that the settings in µVision under Project - Options for Project - Debugger - Keil Monitor 51 - Settings are COM1 at 38400 baud and that Stop Execution with Serial Interrupt is not checked. You may check Load Program at Startup and Go Until Main if you wish.
  7. Make certain that your application is not violating the memory space of either the monitor or the chip. After verifying these settings, start the µVision Debugger and you should be able to debug.



The following Discussion Forum threads may provide information related to this topic.

Last Reviewed: Friday, June 26, 2009

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