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Information in this article applies to:

  • µVision Version 2.20


Projects created and debugged on the Cypress EZ-USB board lose monitor communication when single-stepping through the program. Usually this happens after a sequence of instructions similar to the following:

// PORT setup for output
PORTACFG = 0;    // use all port a pins a IO
PORTBCFG = 0;    // use all port b pins a IO
PORTCCFG = 0;    // use all port c pins a IO
OEC = 255;       // and then all as outputs
OEA = 255;       // and then all as outputs
OEB = 255;       // and then all as outputs


The MON51 Target Monitor uses one of the on-chip UART's on the Cypress chip for communication. The UART's transmit and receive lines are part of PORTB or PORTC depending on the serial port.

In the above example, all I/O pins of Port A, Port B, and Port C are set for output (using the OEA, OEB, and OEC SFRs). This causes the serial port to be unable to receive data from the PC.


Modify only those pins of Port A, B, and C that do not interfere with the serial port.


  • Refer to Application Note 162 which shows how to program and debug applications with the Cypress EZ-USB Board and the Keil development tools.

Last Reviewed: Tuesday, January 11, 2005

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