Question

Consider a hypothetical computer with an instruction set of only two n-bit instruc- tions.The first bit specifies the opcode, and the remaining bits specify one of the 2-1 n-bit words of main memory. The two instructions are as follows: 12.7 SUBS X Subtract the contents of location X from the accumulator, and store the result in location X and the accumulator. Place address X in the program counter JUMPX A word in main memory may contain either an instruction or a binary number in twos complement notation. Demonstrate that this instruction repertoire is reason- ably complete by specifying how the following operations can be programmed: a. Data transfer: Location X to accumulator, accumulator to location X b. Addition: Add contents of location X to accumulator c. Conditional branch. d. Logical OR. e. LO Operations.

Answer 1

(a Data trans^r: Locol?or x to accumolao acc mutov to Location X kee P Locations y, 2 as scratch space conch uoe using LS can move X Zero occomulotor Volue 3ulbs z sulb s z ., zevo occomulo Value ator Jeaer and copy-lo a cconmu Subs x; Re g tar, subs x ', zero accumulator and x value subs 2 accumulator Subs 2', pul zero ln z value subs or?afnal Value boek tox and GCcUmulator

Add Contents of Loca fonx to accumubfor Add ts 3ame as alte an accurmulator substrac4 x Value 3ubs y , a gulbs z . zero out occumulator and z 3ubs z SubS and accumulator ane -ve Oraşvol tone accumulatorn y and accumulator aue ve +h sun o oiainal Value Subs 2 gubs x eetaue x value gulbs 2 vatues