Interrupt Control Functions, Mode 0 Timing

SILICON GATE MOS 8255

CONTROL WORD

r0 7 t0 6 I0 5 10 4 I 0 3 1 O2 I 0, IDO I

I	I	I	L	BIT SET/RESET
I	I	I		1 =SET
,x	X	x,		0:: RESET
	I
	DON'T
	CARE
				BIT SELECT
				o 1 2 3 4 5 6	7

o 1 o 1 o 1 o 1 801

o 0 1 1 o 0 1 1 B,-lo 0 o 0 1 1 1 1 B21

BIT SET/RESET FLAG

Om ACTIVE

When Port C is being used as status/control for Port A or B, these bits can be set or reset by using the Bit Set/Reset op- eration just as if they were data output ports.

Interrupt Control Functions

When' the-' 8255 is programmed to operate in Mode 1 or Mode 2, control signals are provided that can be used as interrupt request inputs to the CPU. The interrupt request signals, generated from Port C, can be inhibited or enabled by setting or resetting the associated INTE flip-flop, using the' Bit set/reset function of Port C.

This function allows the Programmer to disallow or allow a

.specific I/O device to interrupt the CPU without effecting any other device in the interrupt structure.

INTE flip-flop definition:

Bit Set/Reset Format

Operating Modes

Mode 0 (Basic Input/Output)

This functional configuratioD provides simple .1 nput and Output operations for each ,of the three ports. No "hand- shaking" is required, data is simply written to or read from a specified port.

(BIT-SET) - INTE is SET - Interrupt enable (BIT-RESET) - INTE is RESET - Interrupt disable

Note: All Mask flip-flops are automatically reset during mode selection and device Reset.

Mode 0 Basic Functional Definitions:

•Two 8-bit ports and two 4-bit ports.

•Any port can be input or output.

•Outputs are latched.

•Inputs are not latched.

•16 different Input/Output configurations are possible in this Mode.

BASIC INPUT

TIMING (07-00

FOLLOWS INPUT, INPUT

NO LATCHING)

tDELAYTIME	t DELAY TIME
FROM RD	---------FROM INPUT DATA

	-------X	X------
BASIC OUTPUT	~ SET·UPVIOLATION
TIMING (OUTPUTS	-------	------
LATCHED)	-------	------
LATCHED)

OUTPUT

tDATA - .

SET·UP

Mode 0 Timing

5-117

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 Interrupt Control Functions, Operating Modes Mode 0 Basic Input/Output, Mode 0 Timing

Models: 8080