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Target (Keil C51)

Xtal (MHz)
Specifies the CPU clock of your device. In most cases this value is identical with the XTAL frequency.
Memory Model
Specifies the C51 compiler memory model. For starting new applications the default SMALL is a good choice.
Code Rom Size
Specifies the size of the program memory. This directive affects the coding of the JMP and CALL instructions.
Operating system
You may use an real-time operating system in your application. Keil offers two different versions:
  • RTX51 Tiny is part of the PK51 Professional Developers Kit and typically the best choice for 8051 applications. RTX51 Tiny works even on the smallest systems and supports round-robin task switching, supports signal passing and can be operated with interrupt functions in parallel.
  • RTX51 Full supports both round-robin and preemptive task switching. RTX51 Full provides signal passing; message passing with a mailbox system and semaphores.
Use On-chip ...
Specify the usage of the on-chip components which are typically enabled in the CPU startup code or at beginning of the main function. Make sure that the dialog settings are identical with the configuration of the startup file or the device initialization (see also Note below).
Off-chip ... memory
Specify the external CODE and XDATA memory areas of the target hardware (see also Note below).
When using Monitor-51 the CODE and XDATA areas must be non-overlapping physical memory. For Monitor-51 the application code is stored in von Neumann mapped RAM (means that CODE and XDATA are identical; required since the 8051 cannot write to CODE).
Code Banking
Enables program code banking and allows to define the number of Code Banks and the start and end address supported by your hardware. To locate program code into a code bank the source modules must be assigned in the dialog Options — Properties to a code bank. A code banking configuration file such as L51_BANK.A51 is required to configure the banking hardware.
'far' memory type support
Far memory allows to expand the physical XDATA space by using different methods. Example projects can be found in the folder ..\C51\Examples\FarMemory. Extended 8051 devices provide typically additional CPU instructions. For classic 8051 devices the files XBANKING.A51 and L51_BANK.A51 allow configuration of the banking hardware.
Save address extension SFR in interrupts
In some configuration it is required to save the address extension SFR at the beginning of interrupt service routines.


  • For automatic linker configuration the option Use Memory Layout from Target Dialog in the Linker Locate dialog page must be enabled.
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