Symbols and Abbreviations, Description Format, All

Auxiliary Carry: If the instruction caused a carry out of bit 3 and into bit 4 of the resulting value, the auxiliary carry is set; otherwise it is reset. This flag is affected by single precision additions, subtractions, incre- ments, decrements, comparisons, and log- ical operations, but is principally used with additions and increments preceding a DAA (Decimal Adjust Accumulator) instruction.

Symbols and Abbreviations:

The following symbols and abbreviations are used in the subsequent description of the 8080 instructions:

SYMBOLS	MEANING
accumulator	Register A
addr	16-bit address quantity
data	8-bit data quantity
data 16	16-bit data quantity
byte 2	The second byte of the instruction
byte 3	The third byte of the instruction
port	8-bit address of an I/O device
r,rl,r2	One of the registers A,B,C,D,E,H,L
DDD,SSS	The bit pattern designating one of the regis-
	ters A,B,C,D,E,H,L (DDD=destination, SSS=
	source):
	DOD or SSS REGISTER NAME
	111	A
	000	B
	001	C
	010	D
	all	E
	100	H
	101	L
rp	One of the register pairs:
	B represents the B,C pair with B as the high-
	order register and C as the low-order register;
	D represents the D,E pair with D as the high-
	order register and E as the low-order register;
	H represents the H,L pair with H as the high-
	order register and L as the low-order register;
	SP represents the 16-bit stack pointer
	register.
RP	The bit pattern designating one of the regis-
	ter pairs B,D,H,SP:
	RP	REGISTER PAIR
	00	B-C
	01	D-E
	10	H-L
	11	SP

	rh	The first (high-order) register of a designated
		register pair.
	rl	The second (low-order) register of a desig-
		nated register pair.
	PC	16-bit program counter register (PCH and
		PCl are used to refer to the high-order and
		low-order 8 bits respectively).
	SP	16-bit stack pointer register (SPH and SPL
		are used to refer to the high-order and low-
		order 8 bits respectively).
	rm	Bit m of the register r (bits are number 7
		through afrom left to right).
	Z,S,P,CY,AC	The condition flags:
		Zero,
		Sign,
		Parity,
		Carry,
		and Auxiliary Carry, respectively.
	( )	The contents of the memory location or reg-
		isters enclosed in the parentheses.
		"1 s transferred to"
	/\	Logical AND
	V	Exclusive 0 R
	V	Inclusive OR
	+	Addition
		Two's complement subtraction
	*	Multiplication
	*	"Is exchanged with"
		"Is exchanged with"
		The one's complement (e.g., (A))
	n	The restart number athrough 7

NNNThe binary representation 000 through 111 for restart number 0 through 7 respectively.

Description Format:

The following pages provide a detailed description of the instruction set of the 8080. Each instruction is de- scribed in the following manner:

1.The MAC 80 assembler format, consisting of the instruction mnemonic and operand fields, is printed in BOLDFACE on the left side of the first line.

2.The name of the instruction is enclosed in paren- thesis on the right side of the fi rst line.

3.The next line(s) contain a symbolic description of the operation of the instruction.

4.This is followed by a narative description of the operation of the instruction.

5.The following line(s) contain the binary fields and patterns that comprise the machine instruction.

4-3

8080 specifications

The Intel 8085 and 8080 microprocessors were groundbreaking innovations in the world of computing, paving the way for future microprocessor development and personal computing.

The Intel 8080, introduced in 1974, was an 8-bit microprocessor that played a fundamental role in the early days of personal computing. With a 16-bit address bus, it had the capability to address 64 KB of memory. Running at clock speeds of 2 MHz, the 8080 was notable for its instruction set, which included 78 instructions and 246 opcodes. It supported a range of addressing modes including direct, indirect, and register addressing. The 8080 was compatible with a variety of peripherals and played a crucial role in the development of many early computers.

The microprocessor's architecture was based on a simple and efficient design, making it accessible for hobbyists and engineers alike. It included an 8-bit accumulator, which allowed for data manipulation and storage during processing. Additionally, the 8080 featured registers like the program counter and stack pointer, which facilitated program flow control and data management. Its ability to handle interrupts also made it suitable for multitasking applications.

The Intel 8085, introduced in 1976, was an enhancement of the 8080 microprocessor. It maintained a similar architecture but included several key improvements. Notably, the 8085 had a built-in clock oscillator, simplifying system design by eliminating the need for external clock circuitry. It also featured a 5-bit control signal for status line management, which allowed for more flexible interfacing with peripheral devices. The 8085 was capable of running at speeds of up to 3 MHz and had an extended instruction set with 74 instructions.

One of the standout features of the 8085 was its support for 5 extra instructions for stack manipulation and I/O operations, which optimized the programming process. Additionally, it supported serial communication, making it suitable for interfacing with external devices. Its 16-bit address bus retained the 64 KB memory addressing capability of its predecessor.

Both the 8080 and 8085 microprocessors laid the groundwork for more advanced microprocessors in the years that followed. They demonstrated the potential of integrated circuits in computing and influenced the design and architecture of subsequent Intel microprocessors. Their legacy endures in the way they revolutionized computing, making technology accessible to a broader audience, and their influence is still felt in the design and architecture of modern microprocessors today.