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Information in this article applies to:

  • C51 Version 7.00 or higher
  • µVision Version 2.35 or higher


I'm developing an application for Philips devices. I am using the Philips device in clock doubler mode (X2 = 6 clock cycles per machine cycle) as pre-programmed from Philips. How is the simulator configured for these devices.


Philips offers two ways to configure a device in X2 mode.

  • Philips P89C51RA2H, P89C51RB2H, P89C51RC2H, and P89C51RD2H: these devices have a Flash X2 bit which can be programmed only with a parallel programmer. The simulator therefore has an additional VTREG X2 that is checked on CPU reset. The default value for these devices is X2=1 (6 clock mode) which matches the pre-programmed value from Philips. The 12 clock mode can be selected by X2=0 and performing a Reset.
  • Philips P89C51RA2, P89C51RB2, P89C51RC2, and P89C51RD2: in addition to the VTREG X2, these devices have an additional CKCON SFR register that contains the X2 bit. The VTREG X2 represents the Flash FX2 bit that allows you to run the device in X2 mode all the time.

You may set the VTREG X2 in a debugger INI file as described below:

  1. Create a debugger INI file that sets contains the following commands:
    X2 = 1          /* set X2 mode */
    reset                /* perform CPU reset: uses value at PE_SWD */
    g, main              /* execute program till main */
  2. Under Options for Target -> Debug -> Use Simulator, disable the option "Go til main ()" then enter the filename for the debugger INI file you created.


Last Reviewed: Thursday, April 15, 2004

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