Intel 8080 Processor The 8080 was an 8-bit processor Registers hold 8-bits of information The ALU is capable of doing computations on 8-bit data values Used 16 address lines Address Bus = 16 wires Data Bus = 8 wires System Bus CPU Memory Unit Control Bus

64K Intel 8080 Processor Question: How much memory could be installed in a computer system which uses the 8080 processor? 64K 16 address lines 216 = 65,536 = 64K First address is 0 and the last address is 65,535 So range of addresses is 0H to FFFFH (0FFFFH) Why 64K? Most computers had about 4K of memory (memory was expensive!) Wanted to allow room for growth in the industry “64K is more memory than anyone will ever need!”

Intel 8080 Processor The addressing was simple! Example: Read the contents of memory cell #24,263 Put the address into the MAR This selects the appropriate memory cell Issue the read command to the memory unit Memory unit responds by putting cell’s contents on data bus Memory tells CPU data is ready (using an interrupt) CPU picks up data and stores it in MBR Memory Unit CPU 0000 0001 0002 . . . . 5EC5 5EC6 5EC7 FFFD FFFE FFFF A6 Other Registers MAR MBR 7E Address bus Data bus Control bus F0 5EC6 49 2C 2C 2C 9D ALU 8A Internal Bus 51 9B

General CPU Architecture MAR General Purpose Registers Address Bus to memory & I/O devices 1 2 3 4 MBR Data Bus 1 2 3 4 5 6 7 8 9 Program Counter Instruction Register ALU

General CPU Architecture MAR General Purpose Registers Address Bus 1 2 3 4 MBR Data Bus 1 2 3 4 5 6 7 8 9 Program Counter Instruction Register ALU

Program to add 4 + 7 Instruction 1: Fetch 1 2 3 4 1 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 1 2 3 4 MBR Data Bus Put 4 into 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 1 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 4 into in mem 9 Stop

Instruction 1: Fetch - Complete! 1 1 2 3 4 1 2 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 1 1 2 3 4 MBR Data Bus register 1 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 1 2 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 4 into register 1 in mem 9 Stop

Instruction 1: Execute - Complete! 1 2 3 4 4 2 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 1 2 3 4 4 MBR Data Bus 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 2 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 4 into register 1 in mem 9 Stop

Instruction 2: Fetch 2 1 2 3 4 4 3 2 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 2 1 2 3 4 4 MBR Data Bus Put 7 into 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 3 2 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 7 into in mem 9 Stop

Instruction 2: Fetch - Complete! 3 1 2 3 4 4 3 4 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 3 1 2 3 4 4 MBR Data Bus register 2 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 3 4 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 7 into register 2 in mem 9 Stop

Instruction 2: Execute - Complete! 1 2 3 4 4 7 4 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 1 2 3 4 4 MBR Data Bus 7 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 4 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Put 7 into register 2 in mem 9 Stop

Instruction 3: Fetch 4 1 2 3 4 4 7 4 5 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 4 1 2 3 4 4 MBR Data Bus 7 Add reg 1 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 4 5 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Add reg 1 in mem 9 Stop

Instruction 3: Fetch - Complete! 5 1 2 3 4 4 7 6 5 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 5 1 2 3 4 4 MBR Data Bus 7 and reg 2 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 6 5 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Add reg 1 and reg 2 in mem 9 Stop

Instruction 3: Execute - Complete! 1 2 3 4 4 7 11 6 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 1 2 3 4 4 MBR Data Bus 7 11 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 6 register 2 Add reg 1 Instruction Register ALU and reg 2 ADD Store reg 3 Add reg 1 and reg 2 in mem 9 Stop

Instruction 4: Fetch 6 1 2 3 4 4 7 11 6 7 1 2 3 4 5 6 7 8 9 MAR General Purpose Registers Address Bus 6 1 2 3 4 4 MBR Data Bus 7 Store reg 3 11 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 6 7 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Store reg 3 in mem 9 Stop

Instruction 4: Fetch - Complete! 7 1 2 3 4 4 7 11 8 7 1 2 3 4 5 6 7 8 MAR General Purpose Registers Address Bus 7 1 2 3 4 4 MBR Data Bus 7 in mem 9 11 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 8 7 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Store reg 3 in mem 9 in mem 9 Stop

Instruction 4: Execute - Complete! 9 1 2 3 4 4 7 11 11 8 11 1 2 3 4 5 MAR General Purpose Registers Address Bus 9 1 2 3 4 4 MBR Data Bus 7 11 11 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 8 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Store reg 3 in mem 9 in mem 9 Stop 11

Instruction 5: Fetch - Complete! 8 1 2 3 4 4 7 11 8 11 1 2 3 4 5 6 7 8 MAR General Purpose Registers Address Bus 8 1 2 3 4 4 MBR Data Bus 7 Stop 11 1 2 3 4 5 6 7 8 9 Put 4 into Program Counter register 1 Put 7 into 8 register 2 Add reg 1 Instruction Register ALU and reg 2 Store reg 3 Stop in mem 9 Stop 11