Intel MCS-80/85 manual Data and Instruction Formats

inter 8080Al8080A·1/8080A·2

INSTRUCTION SET

The accumulator group instructions include arithmetic and logical operators with direct, indirect, and immediate ad- dressing modes_

Move, load, and store instruction groups provide the ability to move either 8 or 16 bits of data between memory, the six working registers and the accumulator using direct, in- direct, and immediate addressing modes.

The ability to branch to different portions of the program is provided with jump, jump conditional, and computed jumps. Also the ability to call to and return from sub- routines is provided both conditionally and unconditionally. The RESTART (or single byte call instruction) is useful for interrupt vector operation.

Double precision operators such as stack manipulation and double add instructions extend both the arithmetic and interrupt handling capability of the 8080A. The ability to

increment and decrement memory, the six general registers and the accumulator is provided as well as extended incre- ment and decrement instructions to operate on the register pairs and stack pointer. Further capability is provided by the ability to rotate the accumulator I~ft or right through or around the carry bit.

Input and output may be accomplished using memory ad- dresses as I/O ports or the directly addressed I/O provided for in the 8080A instruction set.

The following special instruction group completes the 8080A instruction set: the NOP instruction, HALT to stop pro- cessor execution and the DAA instructions provide decimal arithmetic capability. STC allows the carry flag to be di- rectly set, and the CMC instruction allows it to be comple- mented. CMA complements the contents of the accumulator and XCHG exchanges the contents of two 16-bit register pairs directly.

Data and Instruction Formats

Data in the 8080A is stored in the form of 8-bit binary integers. All data transfers to the system data bus will be in the same format.

I D7 D6 D5 D4 D3 D2 D1 Dol

DATA WORD

The program instructions may be one, two, or three bytes in length. Multiple byte instructions must be stored in successive words in program memory. The instruction formats then depend on the particular operation executed.

	One Byte Instructions					TYPICAL INSTRUCTIONS
ID7 D6 D5 D4		D3	D2	DtYDJ OP CODE		Register to register, memory refer-
						ence, arithmetic or logical, rotate,
						return, push, pop, enable or disable
						Interrupt instructions
	Two Byte Instructions
ID7 D6 D5 D4	D3	D2	D1	Do I OP CODE
ID7 D6 D5 D4		D3	D2	D1	Do I OPERAND	Immediate mode or I/O instructions
	Three Byte Instructions
I D7 D6 D5 D4	D3	D2	D1	Do I OP CODE	Jump, call or direct load and store
ID7 D6 D5 D4 D3 D2				D1	Do I LOWADDRESSOR OPERAND 1	instructions
ID7 D6 D5 D4 D3 D2				D1	Do I HIGH ADDRESSOR OPERAND 2

For the 8080A a logic "1" is defined as a high level and a logic "0" is defined as a low level.

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