Counting the number of positive and negative number in a data set

Explanation

This 8051 microcontroller assembly code is designed to count positive and negative numbers within a predefined data set stored in memory. The program initializes several registers: R0 points to the starting memory address of the data (30h), R1 acts as a loop counter for 10 numbers, R2 stores the count of positive numbers, and R3 stores the count of negative numbers. Both R2 and R3 are initialized to zero.

The code then enters a loop (LOOP). Inside the loop, it fetches a number from the memory location pointed to by R0 into the accumulator (A). It then checks the Most Significant Bit (MSB) of the accumulator (ACC.7). In 8-bit signed number representation, if the MSB is '1', the number is negative; if it's '0', the number is positive or zero.

If ACC.7 is '1' (meaning the number is negative), the program jumps to the NEGATIVE label, where it increments the R3 (negative count) register. If ACC.7 is '0' (meaning the number is positive or zero), the program falls through to the POSITIVE label, where it increments the R2 (positive count) register. After incrementing the respective counter, a SJMP NEXT instruction ensures that the program skips over the NEGATIVE block if it was a positive number, preventing double counting.

Finally, R0 is incremented to point to the next number in memory, and R1 (the number counter) is decremented. The DJNZ R1, LOOP instruction checks if R1 is zero; if not, it jumps back to the LOOP label to process the next number. This process repeats 10 times until all numbers from 30h to 39h have been processed.

Once the loop finishes, the final count of positive numbers stored in R2 is moved to memory location 40h, and the final count of negative numbers stored in R3 is moved to memory location 50h. The END directive marks the end of the assembly source file.

Algorithm

The algorithm used in this code can be described as follows:

1. Initialization:
   • Set a pointer (R0) to the starting memory address of the data (30h).
   • Initialize a loop counter (R1) to 10 (for 10 numbers).
   • Initialize a positive number counter (R2) to 0.
   • Initialize a negative number counter (R3) to 0.
2. Loop Execution (for 10 numbers):
   • Fetch the number from the memory location pointed to by R0 into the accumulator (A).
   • Check the Most Significant Bit (MSB) of the number in the accumulator (ACC.7).
   • Conditional Counting:
     • If MSB is '1' (number is negative): Increment the negative number counter (R3).
     • If MSB is '0' (number is positive or zero): Increment the positive number counter (R2).
   • Move the memory pointer (R0) to the next location.
   • Decrement the loop counter (R1).
   • If the loop counter (R1) is not zero, repeat from step 2.
3. Store Results:
   • Store the final positive number count (from R2) into memory location 40h.
   • Store the final negative number count (from R3) into memory location 50h.
4. End Program.