Microcontroller survey

Markets for microcontrollers can run into millions of applications. At these volume the microcontroller is a commodity item and must be optimized so that cost is at minimum. Semiconductor manufacturers have a mind-numbing array of designs that would seem to meet almost any need. Some of the chips listed in this post are no longer in regular production, most are current, and a few are best termed "smokeaware": the dreams of the aggressive marketing department.

4-bit Microcontrollers:-

In a commodity chip, expense is represented more by the volume of package and number of pins. To minimize the pin count and package size, it is necessary that the basic data word-bit count be held to a minimum, still enabling useful intelligence to be implemented.
Although 4-bits, in this era of 64-bit "maximicros" may seems somewhat ludicrous, one must recall that original 4004 microprocessor was a 8-bit device, and all else followed. Indeed in terms of production numbers, 4-bit microcontrollers is today is the most popular microwave.
These 4-bit microcontrollers shown below are generally intended for use in large volumes as 1-chip computers; expanding external memory, while possible, would negate the cost advantage desired. Typically consisting in appliances and toys world wide volume is run into tens of millions.

manufacturer:model	Pins:I/O	Counters	RAM(bytes)	ROM(bytes)	Other features
National:COP420	28:30	1	64	1K	Serial bit and I/O
TI:TMS1000	28:23	_	64	1K	LED display
Toshiba:TLCS47	42:45	2	128	2K	Serial bit and I/O

8-bit microcontrollers:-

8-bit microcontrollers are transition zone between 4-bit, 16-bit and 32-bit microcontrollers. 8-bit microcontrollers are proven to be a very useful in small computing tasks. The application sophistication can also range from simple appliance control to high speed machine control and data collection. For these reason microcontroller vendors have established extensive families of similar models. All of them have common features, but differ in amount of RAM, ROM and other cost sensitive features. Often memory can be expanded to include off-chip ROM and RAM; in some cases, the microcontrollers has no on board ROM at all, or the ROM is an EPROM. The purpose of this diversity is to offer the designer a menu of similar devices that can solve almost any problem. The ROMless or EPROM version can be used by designer to prototype the application, then the designer can order the ROM version in large quantities from factory. Many times the ROM version  is never used. The designer makes the ROMless or EPROM design sufficiently general so that one configuration may be used many times, or because production volumes never justify the cost of a factory ROM implementation. Some families have members with fewer external pins to shrink the package and cost: others have special features such as A/D and D/A converter on the chip.

manufacturer: Model	Pins:I/O	Counters	RAM(bytes)	ROM(bytes)	Other features
Intel:8048	40:27	1	64	1K	External memory up to 8K
Intel:8051	40:32	2	128	4K	External memory up to 128K, serial port
Motorola:6805	28:20	1	64	1K
Motorola:68HC11	52:40	2	256	8K	Serial port, A/D converter, Watch Dog Timer
Zilog:Z8	40:32	2	128	2K	External memory up to 128K, serial port
Zilog: z8820	44:40	2	272	8K	External memory up to 128K, serial port

16-bit microcontroller:-

8-bit microcontrollers can be used in a variety of applications that involve limited calculations and relatively simple control strategies. As requirement for faster response and sophisticated calculation grows, the 8-bit design begins to hit a limit inherent with byte wide data word. One solution to overcome this problem is to increase clock speed; another is to increase the size of data word. 16-bit microcontrollers have evolved to solve high speed control problems of the type that might typically be confronted in the control of servo mechanisms, such as robot arms, or for digital signal processing(DSP) applications. The designs become much more focused on these type of real-time problems; some generality is lost, but the vendors till try to hit any marketing target they can. These microcontrollers done all of the functions needed for I/O, data communications and timing and counting are done by adding other specialized chips.

manufacturer:model	Pins:I/O	Counters	RAM(bytes)	ROM(bytes)	Other features
Intel 8096	68:30	2	232	8K	External memory up to 64K,ADC, serial port, PWM and WDT
National:HPC16164	68:65	4	512	16K	External memory up to 64K, serial port, ADC, WDT,PWM

The PWM output is useful for controlling motor speed; it can be done using software in the 8-bit units such with the usual loss of time for other tasks. The 16-bit and 32-bit controllers have also been designed to take advantage of High level programming language in expectation that very little assembly language programming will be done when employing these controllers in sophisticated applications.

32-bit Microcontrollers:-

Crossing boundary from 16 to 32-bits involves more than doubling the word size of the computer, software boundaries that seperate dedicated programs from from supervisory programs are also branched. 32-bit designs target robotics, highly intelligent instrumentation, image processing telecommunication, automobiles and other Environments that feature application programs running under operating system.
The design emphasis now switches on features such as RAM, ROM, Timers and peripherals, and serial ports to high speed computation features. The following table describes the general capability of Intel 80960 a 32-bit microcontroller.

Hardware Features	Software Features
132-Pin ceramic package	Efficient procedure calls
20MHz clock	Fault-Handling capacity
32-bit bus	Trace Events
Floating point unit	Global registers
512-bytes instruction cache	Efficient interrupt vector
Interrupt control	versatile addressing