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C51 C Compiler

The Keil C51 C Compiler for the 8051 microcontroller is the most popular 8051 C compiler in the world. It provides more features than any other 8051 C compiler available today.

The C51 Compiler allows you to write 8051 microcontroller applications in C that, once compiled, have the efficiency and speed of assembly language. Language extensions in the C51 Compiler give you full access to all resources of the 8051.

The C51 Compiler translates C source files into relocatable object modules which contain full symbolic information for debugging with the µVision Debugger or an in-circuit emulator. In addition to the object file, the compiler generates a listing file which may optionally include symbol table and cross reference information.


  • Nine basic data types, including 32-bit IEEE floating-point,
  • Flexible variable allocation with bit, data, bdata, idata, xdata, and pdata memory types,
  • Interrupt functions may be written in C,
  • Full use of the 8051 register banks,
  • Complete symbol and type information for source-level debugging,
  • Use of AJMP and ACALL instructions,
  • Bit-addressable data objects,
  • Built-in interface for the RTX51 Real-Time Kernel,
  • Support for dual data pointers on Atmel, AMD, Cypress, Dallas Semiconductor, Infineon, Philips, and Triscend microcontrollers,
  • Support for the Philips 8xC750, 8xC751, and 8xC752 limited instruction sets,
  • Support for the Infineon 80C517 arithmetic unit.
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