Intel 8080 manual Register to regist~r, memory refer, Ence, arithmetic or logical, rotate

SILICON GATE MOS M8080A

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 abil ity 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 MaOaOA. 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 left or right through or arou nd 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 MaOaOA instruction set.

The following special instruction group completes the Ma080A instruction set: the NOP instruction, HALT to stop processor execution and the DAA instructions provide deci- mal 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 M80aOA is stored in the form of 8-bit binary integers. All data transfers to the system data bus will be in the same format.

ID 7 D6 Ds 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 particu lar operation
executed.
One Byte Instructions							TYPICAL INSTRUCTIONS
I0 7	06	05	0 4	03	02	OLDOJ OPCOOE	Register to regist~r, memory refer-
							ence, arithmetic or logical, rotate,
							return, push, pop, enable or disable
							Interrupt instructions
Two Byte Instru·ctions
1 0 7	D6	D5	D4	D3	D2 D, DO I OP CODE
10 7	D6 D5		D4	D3 D2 D1 DO I OPERAND			Immediate mode or I/O instructions
Three Byte Instructions						0 1 DO I OP CODE
1 0 7	D6	Os	04	03	D2		Jump, call or direct load and store
							instructions
1 0 7	D6	Os	04	0 3 O2 D1 DO I LOW ADDRESS OR OPERAND 1
1 0 7	D6	Ds	04	D3	D2	0 1 DO I HIGH ADDRESSOR OPERAND 2

For the M80aOA a logic "1" is defined as a high level and a logic "0" is defined as a low level.

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