Intel 4004

It was the first complete CPU on one chip, and also the first commercially available microprocessor.

1. Intel 4004

2. INTRODUCTION The  Intel 4004  is a 4-bit central processing Unit(CPU) released by intel corporation in 1971 by intel engineers Fedrico Faggin , Ted Hoff and Stanley Mazor . It was the first complete CPU on one chip, and also the first commercially available microprocessor. the Intel® 4004 processor held 2,300 transistors . This was made possible by the use of then-new silicon gate technology allowing a higher number of transistors and a faster speed than was possible before. The intell 4004 chip took the integrated circuit down one step further by placing all the parts that made a computer think ( i.e central processing unit , memory, input and output controls) on one small chip.

3. INTEL 4004

4. Features Maximum  clock rate  was 740  kHz Instruction cycle time: 10.8 µs [16]   ( 8 clock cycles / instruction cycle) Instruction execution time 1 or 2 instruction cycles (10.8 or 21.6 µs), 46300 to 92600 instructions per second. It uses a single  multiplexed  4-bit bus for transferring: 12-bit addresses 8-bit instructions 4-bit data  words Instruction set  contained 46 instructions (of which 41 were 8 bits wide and 5 were 16 bits wide) Register set contained 16 registers of 4 bits each Internal  subroutine   stack , 3 levels deep.

5. INTEL 4004 PIN CONFIGURATION

6. Intel 4004 architectural block diagram

7. Memory Program memory  size is 4 KB. All conditional instructions work within currently selected ROM (256 bytes). Unconditional jump and jump to subroutine instructions can be used to jump to any address. Data memory  size is 640 bytes. RAM access is done in the same way as access to I/O ports. First, a SRC instruction is used to tell the processor what memory address to access, and successive WRM or RDM writes accumulator data to memory or reads data into accumulator. Data memory is separate from program memory. Stack  is 3-level deep (3 x 12-bit registers). Stack is separate from program memory and data memory. Interrupts None. I/O ports 16 4-bit input ports. 16 4-bit output ports. Registers Program counter  (12-bit). Stack registers . There are three 12-bit stack level registers, which is sufficient to implement 3-level deep subroutine calls. Every subroutine call stores return address in one of the stack registers. Contents of the accumulator and the index registers is not preserved. Accumulator  (4-bit). Mainly used for arithmetic and logic operations, as well as for reading and writing data from/to RAM and I/O ports. Index registers . The microprocessor has 16 4-bit registers, that can work in pairs as 8 8-bit registers .

8. ADDRESSING MODES Immediate(4 and 8-bit data) Register Indirect. Register indirect can access data only within current Rom Memory direct Register(4-bit)

9. INSTRUCTION SET 4004 instruction set consists of 46 instructions Arithmatic – add, subtract, increment, decrement Logic-rotate Control transfer- conditional(limited to current ROM), unconditional, call subroutine and return from subroutine. Input/output instructions Other – carry flag operations , decimal adjust, etc. Instruction length can be one or two bytes.