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CPU
Intel 8080
• 40 pins– How does this compare w/ your
breadboard?
• 7 registers• 78 instructions• 65,536 bytes of addressable memory• Programmable stacks
As described in the manual
CPU
Registers
• A-H or 0-7– A was the accumulator (where results were
stored)
• Pairs– Some instructions required certain registers
to be used– I.e. B and C would be used for a certain
instruction
• Has a PSW (1 byte) in register A that stores the state of the machine
CPU
Memory
• 64k possible memory (2^16)• 8 bit cpu (no direct way to handle 16 bits)• Stack pointer– Programmer maintained– Instruction augmented
• Program counter– 16 bits to tell CPU where to get next instruction
• Instructions could be 1,2, or 3 bytes• Cautions against storing data and
instructions together
CPU
Addressing
• Direct– Uses a register
• Immediate– Instruction then address in memory
• Stack– Convention for first / second places to
get memory (pairs)
CPU
Assembly
• Style– Label Code Operand ;Comment
• Data– Hex, Binary, Octal
• Instructions–+,-,*,mod,and,or,not,shr,shl,xor–mvi register address– jmp address
All arithmetic operations assume 2s complement format
CPU
Assembly(2)
• DW,DB,DS– Define a place in memory
• MOV, LDAX, STAX (Load/Store register A)
• CMP = Compare register / memory w/ register A
• DAD – The double add (16 bit on an 8 bit)
• Many others, but same complexity level
CPU
Stack
• push registerPair• pop registerPair• inx register (increment pointer)
Put / Store registers / memory
CPU
Capabilities?
• What can a 2 Mhz CPU do?
Not an intel CPU.However 1.76Mhzand ~15 MMapped registers