SILICON GATE MOS 8255

MODE DEFINITION SUMMARY TABLE

 

 

MODE 0

MODE 1

MODE 2

 

 

IN

OUT

IN

OUT

GROUP A ONLY

 

PAO

IN

OUT

IN

OUT

~

•

 

PA1

IN

OUT

IN

OUT

•

•

 

PA2

IN

OUT

IN

OUT

...

~

 

PA3

IN

OUT

IN

OUT

...

...

 

PA4

IN

OUT

IN

OUT

•

•

 

PAS

IN

OUT

IN

OUT

...

~

 

PAe

IN

OUT

IN

OUT

~

•

 

PA7

IN

OUT

IN

OUT

...

~

 

PBO

IN

OUT

IN

OUT

--

 

P81

IN

OUT

IN

OUT

--

 

PB2

IN

OUT

IN

OUT

--

 

PB3

IN

OUT

IN

OUT

--

MODE 0

PB4

IN

OUT

IN

OUT

--

OR MODE 1

PB5

IN

OUT

IN

OUT

--

ONLY

PBe

IN

OUT

IN

OUT

--

 

PB7

IN

OUT

IN

OUT

--

 

PCO

IN

OUT

INTRB

INTRB

 

I/O

 

PC,

IN

OUT

IBFB

OBFB

 

I/O

 

PC2

IN

OUT

STBB

ACKB

 

I/O

 

PC3

IN

OUT

INTRA

INTRA

 

INTRA

 

PC4

IN

OUT

STBA

I/O

 

STBA

 

PCS

IN

OUT

IBFA

I/O

 

'IBFA

 

PC6

IN

OUT

I/O

ACKA

 

ACKA

 

PC7

IN

OUT

I/O

OBFA

 

OBFA

 

Special Mode Combination Considerations

There are several combinations of modes when not all of the bits in Port C are used for control or status. The remaining bits can be used as follows:

If Programmed as Inputs -

All input lines can be accessed during a normal Port C read.

If Programmed as Outputs -

Bits in C upper (PC7-PC4) must be individually accessed using the bit set/reset function.

allows the programmer to test or verify the "status" of each peripheral device and change the program flow accordingly..

There is no special instruction to read the status informa- tion from Port C. A normal read operation of Port C is executed to perform this function.

INPUT CONFIGURATION

 

Os

0 3

Do

I

 

i

GROUP A

 

GROUPS

Bits in Clower (PC3-PCO) can be accessed using the bit set/reset function or accessed as a threesome by writing into Port C.

Source Current Capability on Port B and Port C

Any set of eight output buffers, selected randomly from Ports Band C can source lmA at 1.5 volts. This feature allows the 8255 to directly drive Darlington type drivers and high-voltage 'displays that require such source current.

 

 

OUTPUT CONFIGURATION

 

 

0 7

0 6

Os

0 4

0 3

O2

0 1

Do

 

 

i

 

 

 

i

 

 

 

GROUP A

 

 

 

GROUPB

 

Mode 1 Status Word Format

Reading Port C Status

In Mode 0, Port C transfers data to or from the peripheral device. When the 8255 is programmed to function in Modes 1 or 2, Port C generates or accepts "hand-shaking" signals with the peripheral device. Reading the contents of Port C

i

i

GROUP A

GROUP B

(DEFINED BY MODE 0 OR MODE 1 SELECTION)

Mode 2 Status Word Format

5·126

Page 193 Page 195
Page 194
Image 194
Intel 8080 Special Mode Combination Considerations, Source Current Capability on Port B and Port C, Reading Port C Status
Page 193 Page 195

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.
Top Page Image Contents