NAR 1

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NAR 1 processor has a 5-bit address bus (32 bytes of addressable memory) and 8-bit data bus. Machine instructions were single-byte with three most significant bits specifying the opcode and 6 least significant bits the parameter - memory address. A single 8-bit accumulator register was available and there were no flags or flag registers. Only absolute addressing mode was available and all others were achieved by self-modifying code. Following opcodes were available:

• MUA (sr. Memorija U Akumulator, en. Memory Into Accumulator) loads the content of memory location specified by the address parameter into the accumulator
• AUM (sr. Akumulator U Memoriju, en. Accumulator Into Memory) stores the content of the accumulator into memory location specified by the address parameter
• SAB (sr. Saberi, en. Add) loads the content of memory location specified by the address parameter, adds it to the current value of the accumulator and stores the result into the accumulator
• ODU (sr. Oduzmi, en. Subtract) loads the content of memory location specified by the address parameter, subtracts it from the current value of the accumulator and stores the result into the accumulator
• NES (sr. Negativni Skok, en. Negative Jump) performs a conditional jump to the address specified by the parameter if the current value of the accumulator is negative
• ZAR (sr. Zaustavi Računar, en. Stop the Computer) stops any further processing; this is the only instruction that ignores the parameter.

Two more instructions were optional (ie. their functioanlity can be achieved otherwise):

• BES (sr. Bezuslovni Skok, en. Unconditional Jump) performs an unconditional jump to the address specified by the parameter
• NUS (sr. Nula-Skok, en. Zero Jump) performs a conditional jump to the address specified by the parameter if the current value of the accumulator is zero

Trivia

• Word "nar" means Pomegranate in Serbian language
• Many NAR 1 simulators were created. One was named "Šljiva" (en. plum) as that fruit grows in Serbia, while "nar" does not.
• One of frequently given taks was to create a program that adds as many numbers as possible, having those numbers stored in 32-byte memory along with the program. The record was 18 bytes.

See also

• NAR 2

and

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