7.2. MICROCONTROLLER

Microcontroller is an electronic device, similar to a computer, is intended to replace the man in control of the production process, or nearly the entire production process.

From daily practice in the use of computers and meant for the general type of PC is already known that the standard keyboard and mouse input (possibly a joystick), while the standard output monitor or printer. It's hard to define what will be the standard input and output of the microcontroller. The reason is that microcontrollers are usually designed for specific tasks with highly variable from case to case. There are many examples, from simple lighting control, alarm systems, and given control of robots in industrial plants.

The inputs can be quite simple construction, such as the float switch in the highest or lowest monitoring liquid level in the tank. Microcontroller then has to handle only two states described by one bit. Figuring monitoring should be monitored if the actual level of the liquid level in the tank. Then you have to define the level of the track, and they will use a potentiometer circuit microcontroller to deliver a specific analog value which will be followed by the A/D converter to process and deliver the destination. If the turn is associated with a photocell to count the items on the principle of interrupting the light beam it is a direct counting pulses during operation independent of time.

Thus, the ports can be analog and the digital nature of the data and in essence will deliver a measurement transducer (sensor).

Outputs from the microcontroller can also be analog and digital nature. Analog outputs, either voltage or current, electromechanical assemblies can be converted into a useful act as a change in position of an object, increasing the engine speed and the like. The simplest example is a warning light that alerts the person to change or malfunction. Output will be more complex when you want to monitor any changes in size as an analog or digital display.

Of course, the input and output of the microcontroller is not exclusively related to communication with the machine. Very rarely does a controller communication by the user, for example with the lights or digital indicator. But sometimes there is that to communicate with humans using a computer type PC.

From the above it can be concluded that the microcontroller according to the method of making and communication with the environment can be classified into one of two categories:

• Microcontroller as an independent control unit
• Microcontroller as a special card in one slot of a PC

In essence, the microcontroller operates on the principle very close to the computer. He is in truth a little computer, and the complexity it depends on the complexity of the task that has to monitor. General block diagram of microcontroller might look the following picture.

Figure 7.2.1 Block-scheme of microcontroller.

Which will contain all of the elements and how powerful will depend on its purpose. CPU is simpler than the circuits designed PC configuration, usually once-popular Zilog Z80 or some of the family's INTEL processors. To all have common traits:

• Relatively small clock speed of order 10 MHz
• A small number of simple instructions, of order around 100
• Working memory (RAM) of order kB
• Nonvolatile memory with programming code in PROM or EPROM version
• Counters for various purposes such as clocks, pulse counter, BCD counter and other
• Counter for monitoring proper operation - WDT (Watch Dog Timer)
• Input / Output channels (port) for receiving and sending data
• A/D and D/A converters definition of purpose, a common 8-bit
• Wide range of supply voltage

All these elements are not necessarily represented in the microcontroller. The purpose of the microcontroller will depend his choice, and some will have more I / O port's, and another more multiplexed A/D converters and the like. Intel's series microcontrollers MSC-48 has 8 primary by representatives of different possibilities. Apart from these, there are several series of the same manufacturer. If we added the other manufacturers (Motorola, Microchip Technology, Siemens and others) the choice of microcontroller is more than sufficient. A typical representative of the Motorola's microcontroller SAB 80535 described in the example.

Of significance is the WDT control system. It is specially designed counters. If the program is written to memory microcontroller is working properly it will periodically at appropriate intervals (up to 100ms) to return control to the initial value of the counter. If you turn in your work counter counts down to the end, last number placed on the CPU microcontroller knowledge that there had been irregularities in the operation of the program because it was not returned to the initial value. CPU runs a program for re-initialization routine microcontroller or some other place intended protective action. Enough to avoid the long irregular microcontroller regardless of causes for irregularities. This method multiplies the security surveillance system that monitors the microcontroller.

Usually within the device with microcontroller is a small battery life which reaches up to 10 years. Together with the WDT to monitor the correct operation of microcontroller, it follows that the data in RAM will always be preserved, and that the regular maintenance is almost no need. Of course, replace the battery and power the entire assembly in the event of a power failure, similar to what they are doing on-line UPS systems.

Example I

Layout and block diagram Motorola's microcontroller SAB 80535.

Figure 7.2.2 Microcontroller SAB 80535 from Siemens.

This is an eight bit microcontroller unit (CPU) and are available in two versions, 80515 and the 80535. The first contains the program memory (ROM), built-in microcontroller and is made to order with your desired code. The other does not have a built-in memory, but it adds the outside. By other elements are completely identical.

Instruction execution time is one microseconds with clock speed of 12 MHz, which gives a quartz crystal oscillator with added outside the chip. The 256 bytes of internal RAM 128 byte register 41 provided for general motives. Battery and 32 registry dedicate special, and arithmetic and pointing registers and registers for transmission of data between the CPU and peripherals are in another part of the internal RAM. Internal working memory (RAM) and software (ROM) memory can be expanded up to 64 kB additions outside. Will execute code from a work or program memory depends on the situation on the feeder EA (External Access Memory). External memory access is controlled via pin PSEN (Program Store Enable).

There are also performed for the normal and backup power supply and reference voltage and reset the microcontroller and other tasks. Microcontroller has a very elaborate option of ending the program with a total of 12 possible source of interruption with the possible distribution of the 4 priority levels. There is also a 'watchdog' that can be activated using the program but not eliminate.

All six port are 8-bit and two-way. A/D converter is also 8 bit. Works on the principle of successive approximation. The sampling time was 5 microseconds and 20 microseconds conversion time. Of course there is the S&H circuit for memorizing the sample analog signals. Multiplexer takes care of the 8 possible analog inputs to use.

Microcontroller features three 16-bit timers. Each of them can be defined as a classic counter, distributed or something else using the internal or external clock. Microcontroller uses a set of 111 instructions, of which 49 instruction lengths 1 B, 45 instruction lengths 2 B and 17 instruction lengths 3 B. Instructions can be divided into:

• Instructions for transferring
• Arithmetic instructions
• Transmission Control

These data are only part of the other others who are in the manual that is delivered with each microcontroller.

One-chip microcontrollers are developed and marketed using CPU with 4, 8, and 16 bit bus. Proportion of 8-bit microcontrollers is very large (over 50%) in the overall microcontroller market.