PROGRAMMING CONSIDERATIONS

4.5.4Linking Subroutines

Parameters are passed to subroutines via the stack. Parameters are pushed into the stack from the rightmost parameter to the left. The 8-bit parameters are pushed into the stack with the high-order byte undefined. The 32-bit parameters are pushed onto the stack as two 16-bit values; the most- significant half of the parameter is pushed into the stack first. As an example, consider the fol- lowing procedure:

void example_procedure (char param1, long param2, int param3);

When this procedure is entered at run-time, the stack will contain the parameters in the following order:

param3

low word of param2

high word of param2

undefined;param1

 

return address

← Stack Pointer

If a procedure returns a value to the calling code (as opposed to modifying more global variables) the result is returned in the temporary storage space (TMPREG0, in this example) starting at 1CH. TMPREG0 is viewed as either an 8-, 16-, 32-, or 64-bit variable, depending on the type of the procedure.

The standard calling convention adopted by the C programming language has several key fea- tures:

•Procedures can always assume that the eight or sixteen bytes of register file memory starting at 1CH can be used as temporary storage within the body of the procedure.

•Code that calls a procedure must assume that the procedure modifies the eight or sixteen bytes of register file memory starting at 1CH.

•Code that calls a procedure must assume that the procedure modifies the processor status word (PSW) condition flags because procedures do not save and restore the PSW.

•Function results from procedures are always returned in the variable TMPREG0.

The C programming language allows the definition of interrupt procedures, which are executed when a predefined interrupt request occurs. Interrupt procedures do not conform to the rules of normal procedures. Parameters cannot be passed to these procedures and they cannot return re- sults. Since interrupt procedures can execute essentially at any time, they must save and restore both the PSW and TMPREG0.

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Intel 8XC196NP, 80C196NU, Microcontroller manual Linking Subroutines
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Microcontroller, 80C196NU, 8XC196NP specifications

The Intel 8XC196NP and 80C196NU microcontrollers are part of Intel's renowned 16-bit microcontroller series that gained popularity in the 1980s and 1990s for embedded systems applications. Designed for a variety of applications, these microcontrollers are characterized by their robust performance, versatility, and industry-standard architecture.

The 8XC196NP features an enhanced instruction set with over 100 instructions, allowing for efficient code execution. It operates at clock speeds up to 16 MHz, which contributes to improved performance in time-sensitive applications. The microcontroller is equipped with a 16-bit data bus, enabling more efficient data handling compared to its 8-bit predecessors, thus accommodating complex algorithms and large data sets.

In terms of memory architecture, the 8XC196NP supports an addressable memory space of up to 64 KB of program memory and 64 KB of data memory. This configuration provides sufficient space for large applications while ensuring fast data access. The microcontroller includes integrated features such as timers, serial I/O capabilities, and interrupt processing, which enhance its functionality for real-time applications and control mechanisms.

The 80C196NU, on the other hand, is designed for lower power operation, making it suitable for battery-powered devices. This microcontroller maintains similar features to the 8XC196NP while offering advancements that support low-power consumption. The 80C196NU can also function in a range of temperature environments, making it adaptable for industrial applications.

Both the 8XC196NP and 80C196NU support external memory interfacing, allowing designers to expand the system's capability by connecting additional ROM and RAM. This flexibility makes them appealing for developing complex systems, such as motor controls, industrial automation, and consumer electronics.

Another standout feature of these microcontrollers is their built-in debugging capabilities. Intel provided hardware and software tools that enabled developers to test and troubleshoot their applications effectively, reducing the development time and increasing reliability.

Overall, the Intel 8XC196NP and 80C196NU microcontrollers stand out for their dependability, versatility, and performance, contributing significantly to the evolution of embedded system design. Their legacy continues to influence modern microcontroller technology, ensuring their relevance in a wide array of applications today.
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