8051 Microcontrollers...
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Intel's 8031 Architecture

The generic 8031 architecture sports a Harvard architecture, which contains two separate buses for both program and data. So, it has two distinctive memory spaces of 64K X 8 size for both program and data. It is based on an 8 bit central processing unit with an 8 bit Accumulator and another 8 bit B register as main processing blocks. Other portions of the architecture include few 8 bit and 16 bit registers and 8 bit memory locations.

Each 8031 device has some amount of data RAM built in the device for internal processing. This area is used for stack operations and temporary storage of data.

This base architecture is supported with onchip peripheral functions like I/O ports, timers/counters, versatile serial communication port. So it is clear that this 8031 architecture was designed to cater many real time embedded needs.

The following list gives the features of the 8031 architecture:

"        Optimized 8 bit CPU for control applications.
"        Extensive Boolean processing capabilities.
"        64K Program Memory address space.
"        64K Data Memory address space.
"        128 bytes of onchip Data Memory.
"        32 Bi-directional and individually addressable I/O lines.
"        Two 16 bit timer/counters.
"        Full Duplex UART.
"        6-source / 5-vector interrupt structure with priority levels.
"        Onchip clock oscillator.

Now you may be wondering about the non mentioning of memory space meant for the program storage, the most important part of any embedded controller. Originally this 8031 architecture was introduced with onchip, 'one time programmable' version of Program Memory of size 4K X 8. Intel delivered all these microcontrollers (8051) with user's program fused inside the device.
8051 Derivatives

Along the way, this 8031 architecture gained enviable market acceptance. Many semiconductor manufacturers started either manufacturing the 8031 devices as such (Intel was liberal in giving away license to whoever asked) or developing a new kind of microcontrollers based on 8031 core architecture.
Manufacturers modified the basic 8031 architecture and added many new peripheral functions to make them attractive to the designers.

Because of the rush, electronic community started getting a variety of 8031 based devices with range of options. To beat the competition, manufacturers developed different microcontrollers with many unique features.

These parts are popularly known as '8031 Derivatives'. Almost every decent manufacturer boasted of having an 8031 based microcontroller in the line card.

First major manufacturer was the Philips who brought out more than 40-50 derivatives with a variety of I/O options, memory combinations, and peripheral functions. Devices became available in regular DIP and SMD packages. With the basic 8031 core, Philips ported high capacity Program Memory (upto 32K/64K), its patented I2C interface bus, 8/10 bit Analog to Digital Converters, CAN Bus, Capture and Compare registers, Watch dog timer, PWM facilities and etc. More I/O ports (as many as eight ports), additional timer/counter, second serial port was also made available in Philips devices.

Apart from all these, Philips developed many consumer devices meant for telecom, computer and TV applications. A smart card controller was also developed by incorporating a cryptographic engine. So Philips clearly established itself as the market leader in 8031 derivatives and still caters to this segment.

Then came Dallas semiconductor. Dallas redesigned the 8031 architecture and eliminated waste clock cycles of original core and made all instructions executed in less clock cycles (maximum of 4) which has traditionally taken upto 12 clock cycles. So, came the birth of High speed 8031 Derivatives.

Dallas also maintained the same device pin out configurations to enable the user get upto 3X performance by replacing slower parts with a Dallas device. So, existing compiled code started running faster without any modification. These days, you can find Dallas devices giving upto 50 MIPS (Million Instructions Per Second).

Apart from this, Dallas introduced additional Serial port, Watch Dog Timer, Precision Reset Circuitry, Real Time Clock, Power Fail Monitor in the 8031 devices. Also a second data pointer, more onchip RAM space and more interrupt lines were also made available.

Dallas semiconductor also has got a range of secure microcontrollers based on 8031 core. This microcontroller family uses non volatile RAM to keep both program and data. Because of this RAM, the controller gives the In System Reprogrammability. Dallas has combined this microcontroller, SRAM and lithium cell in a single pack. This device guarantees 10+ years of data retention in the RAM area. This 8031 also boasts the tamper proof security features like Real Time Memory Encryption, user selected 48 bit Encryption key, memory contents, security lock and the facility to hide interrupt vector table. As you can agree, this particular 8031 device has found a niche market in banking and security related applications.

Atmel Corporation is the another major semiconductor manufacturer who introduced many flash memory based 8031 derivatives at a competitive cost. Atmel used its expertise in flash memory technology into the basic 8031 core and brought out microcontrollers with a variety of flash memory options and few devices also carry In System Reprogramming facility. You can program/reprogram this microcontroller after soldering the device in the target board. If this programming facility is embedded in the system software, then the tasks like remote calibration, onsite system upgradation become as easy as sending your data/program in a floppy disk or by internet. Atmel devices sport security lock to its flash memory to protect the contents from the prying eyes.

Meantime, Intel itself tried to cash in the popularity of this 8031 architecture and introduced improved versions of microcontrollers: 80151 and 80251 families. These devices sport 16 bit architecture using 8031 core and unfortunately these devices have not become as popular as 8031.Even after many years of introduction, 8031 core is still going strong in 8 bit arena.
Why Atmel Devices

We like Atmel's flash memory very much. In early days, we used to get EPROM devices from 'God - only - knows' sources and we always worried about the life of our target hardware. Atmel really relieved us form this. Without caring about EPROM erases, we can program/reprogram the device during prototype development and most of the time device stays cool even after many hours of running. Also we can go upto 24MHz with these devices using 3V to 6V supply.

Atmel 89C51 Microcontrollers

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4 Kbytes of Flash Programmable and Erasable Read Only Memory (PEROM). The device is manufactured using Atmel's high density nonvolatile memory technology and is compatible with the industry standard MCS-51Ô instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.

The AT89C51 provides the following standard features: 4 Kbytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator
disabling all other chip functions until the next hardware reset.
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