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OTHER SPECIAL FEATURES
WATCHDOG TIMER
A watchdog timer provides a means of graceful recovery from a system problem. System problem could be a program that goes into an endless loop, or a hardware problem that prevents the program from operating correctly. If the program fails to reset the watchdog at some predetermined interval, a hardware reset will be initiated. The bug may still exist, but at least the system has a way to recover. This is especially useful for unattended systems.
DIGITAL SIGNAL PROCESSORS (DSP)
Microcontrollers react to and control events-DSPs execute repetitive math-intensive algorithms. Today many embedded applications require both types of processors, and semiconductor manufacturers have responded by introducing microcontrollers with on-chip DSP capability and DSPs with on-chip microcontrollers.
The most basic thing a DSP will do is a MACC (Multiply and Accumulate). The number of data bits a DSP can multiply and Accumulate will determine the dynamic range (and therefore the application).
CLOCK MONITOR
A dock monitor can shut the microcontroller down (by holding the microcontroller in reset) if the input clock is too slow. This can usually be turned on or off under software control.
RESIDENT PROGRAM LOADER (RPL)
Loads a program by Initializing program/data memory from either a serial or parallel port. RPL is convenient for prototyping or trying out new features, eliminates the erase/burn/program cycle typical with EPROMs, and allows convenient updating of a system even from ar.. offsite location.
MONITOR
A monitor is a program installed in the microcontroller which provides basic development and debug capabilities. Typical capabilities of a microcontroller monitor include: loading object files into system RAM, executing programs. examining and modifying memory and registers, code disassembly, setting breakpoint, and
single- stepping through code. Some simple monitors only allow basic functions such as memory inspection, and the more sophisticated
monitors are capable of a full range of debug functions.
Monitors can either communicate with a dumb terminal or with a host computer such as a PC. Much of the work of the monitor (such as user interface) can be offloaded to the host PC running a program designed to work with the monitor. This makes it possible to reduce the size and complexity of the code that must be installed in the target system.
APPLICATIONS
In addition to control applications such as the home monitoring system, microcontrollers are freqiiently found in embedded applications. Among the many uses that you can find one or more microcontrollers: automotive applications, appliances (microwave oven, refrigerators, television and VCRs, stereos), automobiles (engine control, diagnostics, climate control environmental control (greenhouse, factory, home), instrumentation, aerospace, and thousands of other uses.
Microcontrollers are used extensively in robotics. In this application, many specific tasks might be distributed among a large number of micro controllers in one system. Communications between each microcontroller and a central, more powerful microcontroller (or microcomputer) would enable information to be processed by the central computer, or to be passed around to other microcontrollers in the system.
A special application that microcontrollers are well suited for is data logging. Stick one of these chips out in the middle of a corn field or up in a balloon, and monitor and record environmental parameters (temperature, humidity, rain, etc). Small size, low power consumption, and flexibility make these devices ideal for unattended data monitoring and recording
MICROCONTROLLER TYPES
Microcontrollers come in many flavors and varieties. Depending on the power and features that are needed, one might choose a 4 bit, 8 bit, 16 bit, or 32 bit microcontroller. In addition some specialized versions are available which include features specific for communications, keyboard handling, signal processing, video processing, and other tasks. The examples of different types of microcontrlles are given in Tables.
| Model (Manufacturer)
|
Features
|
| 8048 (Intel)
|
Modified Harvard
architecture with program ROM on chip with an
additional 64 to 256 bytes
of RAM also on chip. I/O is mapped in its
own space.
|
| 8051 (Intel)
|
Modified Harvard architecture with separate address spaces for program memory and data memory. The program memory can be up to 64K. The 8051 can address up to 64K of external data memory, and is accessed only by indirect addressing. The 8051 has 128 bytes of on-chip RAM, plus a number of special function registers (SFRs). I/O is mapped in its own space. The 8051 has features of "boolean processing" . |
| COP800 Family (National)
|
The COP800 Basic Family is a fully static 8-bit microcontroller, fabricated using double metal silicon gate microCMOS technology. Features include: 8-bit memory mapped architect, serial I/O, UART, memory mapped I/O, many 16 bit timer/counters with capture registers, a multi-sourced vectored interrupt, comparator, WATCHDOG Timer and Clock monitor, 8-channel A/D converter with prescaler, brownout protection, halt mode, idle mode etc. |
| 6805 (Motorola)
|
It has a Von-Neuman architecture in which instructions, data, I/O, and timers all share the same space. Stack pointer is 5 bits wide which limits the stack to 32 bytes deep. Some members of this family include on chip A/D, PLL frequency synthesizer, serial I/O etc. |
| 68hcll (Motorola)
|
The 68hcll is a powerful 8-bit data, 16-bit address microcontroller. The 68hc11 has a common memory architecture in which instructions, data, I/O, and timers all share the same memory space. Depending on the variety, the 68hcll has built-in EPROM/OTPROM, RAM, digital I/O, timers, A/D converter, PWM generator, pulse accumulator, and synchronous and asynchronous communications channels. Typical current draw is less than 20ma. |
| TMS370
(Texas Instruments)
|
It is similar to the 8051 in having 256 registers, A and B accumulators, stack in the register page, etc. It has a host of onboard support devices, include: RAM, ROM (mask, OTP, or EEPROM), 2 timers (configurable as timers/ counters/comparators/PWM output), watchdog timer, SCI (synchronous serial port), SPI (asynchronous serial port), A/D (8 bit, 8 channel), interrupts. Instruction set is mostly 8 bit with some 16 bit support. Clock speeds are up to 20MHz which gives 5MHz for buss access and instruction cycles. |
| PIC (MicroChip)
|
The PIC microcontrollers were the first RISC microcontrollers. Having few instructions (eg. 33 instructions for the 16C5X line versus over 90 for the Intel 8048), Separate buses for instructions and data (Harvard architecture) allows simultaneous access of program and data, and overlapping of some operations for increased processing performance. The benefits of design simplicity are a very small chip, small pin count, and very low power consumption. Available in three lines: the PIC16C5x, PIC16xx, and PIC17Cxx families. |
| 80c196 (Intel)
|
The 80c196 is a 16 bit processor. Originally fabricated in NMOS (8096), it is now mainly available in CMOS. Many features it includes are: hardware multiply and divide, 6 addressing modes, high speed I/O, A/D, serial communications channel, up to 40 I/O ports, 8 source priority interrupt controller, PWM generator, and watchdog timer. |
| HPC Family (National)
|
The HPC Family of High Performance microcontrollers is a 16-bit controller fabricated using microCMOS technology. The architecture is a Von-Neuman architecture where the program and data memory share the same address space. Features include: 16-bit memory- mapped architecture with software configurable external address/ data bus, Microwire/Plus serial I/O, UART, 16-bit timer/counters with input capture capability, High-Level Data Link Control (HDLC) for ISO-standard data communications, 8-channel A/D converter with prescaler, power-saving modes, Multiply/Accumulate Unit with built- in circular buffer management for low to medium DSP applications, software configurable chip-select outputs, 64KB address space directly addressable, low-voltage (3.3V) operation. |
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