Simple Computing System(SCS)

The Simple Computing System is a prototype to show the entire working of the computer, in terms of memory, compiler, etc.. Please download the SCS.zip, from step 5, unzip it and run the exe, to understand more clearly what this system does.

1. To start with, the Simple Computing System has an assembly-level programming language. The program in this language is converted into bits, which are used by the Operating System to get the things done. The following instruction set defines the language.

   Source Code	Meaning	Source Code	Meaning
   DIRECT MODE
   Retrieval from and storage to memory
   LDAD xxx	ACC1 = Mem[xxx]	STAD xxx	Mem[xxx] = ACC1
   Operations on accumulator
   ADAD xxx	ACC1 = ACC1 + Mem[xxx]	SBAD xxx	ACC1 = ACC1 - Mem[xxx]
   MULD xxx	ACC1 = ACC1 * Mem[xxx]	DIVD xxx	ACC1 = ACC1 / Mem[xxx]
   MODD xxx	ACC1 = ACC1 % Mem[xxx]	NEGA	ACC1 = -ACC1
   SHRA	Shift ACC1 bits to right	SHLA	Shift ACC1 bits to right
   RTRA	Rotate ACC1 bits to right	RTLA	Rotate ACC1 bits to left
   Operations on memory
   CLRM xxx	Mem[xxx] = 0	INCM xxx	Mem[xxx] = Mem[xxx]+1
   DECM xxx	Mem[xxx] = Mem[xxx]-1	NEGM xxx	Mem[xxx] = -Mem[xxx]
   Jump Instructions
   JUMP xxx	IP = xxx	JMEQ xxx	If EQ = 1 then IP = xxx
   JMNE xxx	If EQ = 0 then IP = xxx	JMLT xxx	If LT = 1 then IP = xxx
   JMGE xxx	If LT = 0 then IP = xxx	JMLE xxx	If(LT = 1 or EQ = 1) then IP = xxx
   JMGT xxx	If(LT = 0 and EQ = 0) then IP = xxx
   JMOV xxx	If OV = 1 then IP = xxx	JMNO xxx	If OV = 0 then IP = xxx
   Setting and Clearing bits
   STOV	OV = 1	CLOV	OV = 0
   STEQ	EQ = 1	CLEQ	EQ = 0
   STLT	LT = 1	CLLT	LT = 0
   Miscellaneous
   NOPN	No operation	HALT	Halt
   Input/Output
   INAC	Get input into ACC1	OUTA	Show ACC1
   INPD xxx	Get input into Mem[xxx]	OUTD xxx	Show Mem[xxx]
   Compare accumulator
   CMPA xxx	If ACC1 = Mem[xxx] then EQ = 1, else EQ = 0; If ACC1 < Mem[xxx] then LT = 1, else LT = 0
   INDIRECT MODE
   Retrieval from memory
   LDAI xxx	ACC1 = xxx
   Operations on accumulator
   ADAI xxx	ACC1 = ACC1 + xxx	SBAI xxx	ACC1 = ACC1 - xxx
   MULI xxx	ACC1 = ACC1 * xxx	DIVI xxx	ACC1 = ACC1 / xxx
   MODI xxx	ACC1 = ACC1 % xxx
   Input/Output
   OUTI xxx	Show xxx
   Compare accumulator
   CMAI xxx	If ACC1 = xxx then EQ = 1, else EQ = 0; If ACC1 < xxx then LT = 1, else LT = 0

   The Registers used are: 6 Accumulators(ACC1 for the user's immediate use, ACC2, ACC3, ACC4, ACC5, ACC6 for internal binary arithmetic), Instruction Pointer(IP), Instruction Register(IR), Operand part register(OPNDW), 5 bits(EQ: equal bit, LT: less than bit, OV: overflow bit, INFLAG: input flag, OUTFLAG: output flag).

2. The user has to enter all the numbers in the decimal format for the ease of use. All the opcodes and operands are then converted into bits. the memory is also organized into bits. All the arithmetic is binary arithmetic, so when the memory or the accumulators are required by to be seen by the user, their contents are shown in equivalent hexadecimal and decimal format. The complete project can thus be used to make the working of computer clear to the students of Assembly Language Programming, Logic Design and even Computer Architecture. The program code for the conversion of source code into object code can also be used for basic Compiler Design courses.

3. The programs can be entered from the console or from the file with the extension ".dgf". This may also send the compile time errors if there are any.

4. The programs can be run in one go or step-by-step. The runtime errors, like division by zero, memory out of bound, etc., are displayed.

5.  You can download the SCS.zip from here. This contains SCS.exe.

6. Run the SCS.exe. On being prompted to enter a file name, enter a file name as "p1.dgf", or "f77.dgf", etc..