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

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.