µVISION DEBUGGER: Serial Interrupt of Monitor does not work

Information in this article applies to:

• µVision 2.34
• Cx51 Compiler, all versions
• C251 Compiler, all versions

QUESTION

I am using the Keil Monitor (MON51, MON251, FLASHMON, and MON390) to debug my application. Although I checked the box Serial Interrupt in the Settings Dialog, the Monitor does not stop and reports a connection error.

How can I solve this error?

ANSWER

There are two things you need to do in your application:

• Reserve the Interrupt vector
  Your application may not write to the serial interface vector. The easiest way to reserve this vector is to locate an array of 3 bytes at a fixed address at the beginning of your C program. Just reserve the serial interrupt of the on-chip interface that your monitor configuration uses.
  • For the standard (or first) onchip UART:

     char code reserve[3] _at_ 0x23;
    

  • For the second onchip UART:

     char code reserve[3] _at_ 0x53;
    

• Enable the interrupt system
  The interrupt system must be enabled with the global EA flag for serial interrupt. The Monitor only initializes the interrupt system, and it does not set the general interrupt flag EA. So you need to set EA in your application, which may look like:

 EA = 1;

Note, the name of the EA register might be different on some 8051 device variants.

SEE ALSO

• MON51: Error 26 (cannot write Interrupt Vector)

Last Reviewed: Thursday, January 7, 2021