Question

III Show RSCPU machine code bytes (in binary) for the assembly code (note that the machine code starts at memory location 0.): 0: LDAC 60 MVAC LDAC 70 SUB STAC 75 IV. Assume a 64-byte memory module connected to a CPU that has a 10-bit address bus. Show the logic to generate the CE signal for this memory module if it occupied the following range of addresses: a) 128 to 191 b) 640 to 703 c) 0 to 63

Answer 1

A)

Following code is used to subtract the contents of memory location 60 and 70 and then store the result in memory location 75

LDAC 60
Loads the content from memory location 60 into CPU's Accumulator (AC)

< OP CODE >   < 16 Bit memory address >
0000 0001 0000 0000 0000 0000 0000 0110 0000 0000

MVAC
Copies the content of AC (Accumulator) to Register R

< OP CODE >  
0000 0011

LDAC 70
Loads the content from memory location 70 into CPU's Accumulator (AC)

< OP CODE >   < 16 Bit memory address >
0000 0001 0000 0000 0000 0000 0000 0111 0000 0000

SUB
Subtract the contents of AC (Accumulator) and R (R Register) i.e. AC = AC - R, if (AC - R = 0) then Z = 1, else Z = 0

< OP CODE >
0000 1001

STAC 75
Store the Contents of Accumulator (AC) in memory location 75

< OP CODE > < 16 Bit memory address >
0000 0010 0000 0000 0000 0000 0000 0111 0000 0101