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C51: Missing Multiple DPTR support for some ATMEL Devices

Information in this knowledgebase article applies to:

  • C51 Version 9.50a and earlier


The µVision dialog Options for Target — Target did not show the option Use multiple DPTR registers for these ATMEL devices:
AT89S4D12, AT87F51RC, AT89C51RC, AT89S51, AT89LS51, AT89S52, AT89LS52, AT89C55WD, AT87F55WD


The µVision device database contained wrong options for these devices.


You can specify the options for dual data pointer support manually in the dialog Options for Target — C51 — Misc Controls. Please use the right directive for your device. Atmel devices have two different methods to switch the DPTR.

MODA2 for:

  • AT89S4D12

MODP2 for:

  • AT87F51RC
  • AT89C51RC
  • AT89S51
  • AT89LS51
  • AT89S52
  • AT89LS52
  • AT89C55WD
  • AT87F55WD


This will be fixed in all C51 versions later than 9.50a. If a project was created with a C51 version 9.50a or before, re-select the device in the Options for Target — Device dialog to apply the new options to your project.


  • Refer to MODP2 in the Cx51 User's Guide.
  • Refer to MODA2 in the Cx51 User's Guide.


Last Reviewed: Friday, November 7, 2014

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