Branch Group, 000 | Intel 8080 manual

CMC	(Complement carry)

(CY)~ (CY)

The CY flag is complemented. No other flags are affected.

a , 0 ,

Cycles: 1

States: 4

Flags: CY

STC	(Set carry)

(CY) ~ 1

The CY flag is set to 1. No other flags are affected.

0 I 0 I

0 I 1

I 1

Cycles: 1

States: 4

Flags: CY

Branch Group:

This group of instructions alter normal sequential program flow.

Condition flags are not affected by any instruction in this group.

The two types of branch instructions are uncondi- tional and conditional. Unconditional transfers simply per- form the specified operation on register PC (the program counter). Conditional transfers examine the status of one of the four processor flags to determi ne if the specified branch is to be executed. The conditions that may be specified are as follows:

CONDITION			CCC
NZ	-	not zero (Z = 0)	000
2	-	zero (2 = 1)	001
NC	-	no carry (CY = 0)	010
C	-	carry (CY = 1)	011
PO	-	parity odd (P = 0)	100
PE	-	parity even (P = 1)	101
P	-	plus (S = 0)	110
M	-minus(S=1)		111
JMP addr		(Jump)

(PC) ~ (byte 3) (byte 2)

Control is transferred to the instruction whose ad-

dress is specified in byte 3 and byte 2 of the current

instruction.

1 I 1 I 0 I 0 I 0 I 0 I 1 I 1

low-order addr

high-order addr

Cycles: 3

States: 10

Addressing: immediate

Flags: none

Jcondition addr

(Conditional jump)

If (CCC),

(PC) ~ (byte 3) (byte 2)

If the specified condition is true, control is trans- ferred to the instruction whose address is specified in byte 3 and byte 2 of the current instruction; other- wise, control continues sequentially.

1 I 1 I C I C I C I 0 I 1 I 0

low-order addr high-order addr

Cycles: 3

States: 10

Addressing: immediate

Flags: none

CALL addr (Call) ((SP) - 1) ~ (PCH)

((SP) - 2) ~ (PCl) (SP) ~ (SP) - 2

(PC) ~ (byte 3) (byte 2)

The high-order eight bits of the next instruction ad- dress are moved to the memory location whose address is one less than the content of register SP. The low-order eight bits of the next instruction ad- dress are moved to the memory location whose address is two less than the content of register SP. The content of register SP is decremented by 2. Con- trol is transferred to the instruction whose address is specified in byte 3 and byte 2 of the current instruction.

1 I 1 I 0 I 0 I 1 T 1 I 0 I 1

low-order addr

high-ord~raddr

Cycles: 5

States: 17

Addressing: immediate/reg. indirect

Flags: none

4-11

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.

Intel 8080 manual Branch Group, 000

Models: 8080

CMC

Branch Group:

000

1 I 1 I 0 I 0 I 0 I 0 I 1 I 1

8080 specifications