Saturday, September 12, 2009

Find the negative numbers in a block of data(8085)

Statement:Find the number of negative elements (most significant bit 1) in a block of data. The length of the block is in memory location 2200H and the block itself begins in memory location 2201H. Store the number of negative elements in memory location 2300H

Sample problem
(2200H) = 04H
(2201H) = 56H
(2202H) = A9H
(2203H) = 73H
(2204H) = 82H
Result = 02 since 2202H and 2204H contain numbers with a MSB of 1.
Source program
LDA 2200H
MOV C, A : Initialize count
MVI B, 00 : Negative number = 0
LXI H, 2201H : Initialize pointer
BACK: MOV A, M : Get the number
ANI 80H : Check for MSB
JZ SKIP : If MSB = 1
INR B : Increment negative number count
SKIP: INX H : Increment pointer
DCR C : Decrement count
JNZ BACK : If count 0 repeat
STA 2300H : Store the result
HLT : Terminate program execution

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