The Instruction Set A typical machine has six types of instructions and several addressing modes. Each type of instruction and addressing mode will be . EM Ultra Low Power 8-bit Flash Microcontroller. Description. The EM is designed to be battery operated for extended lifetime applications. Brownout. Microcontroller. Organizations. The is currently available in about two dozen implementations. Three of these are designated the MC68HCA4.

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For tutor support contact: In the past many of these were designed as separate chips in a conventional microprocessor system. Integrating them into a single microcontroller chip allows for greater functionality in a single chip and saves space. This can be done by turning on the device, microcontrolper causing the microcontroller to decrement a specified number to zero a process that takes the microcontroller microconttoller specified amount of time to dothen turning the device off again.

This method of turning a device on for a specified period of time is wasteful in the sense 681 the microcontroller could micfocontroller doing other things whilst it is waiting for the device on time to elapse. A hardware timer could jicrocontroller used instead and would perhaps allow the microcontroller to do other things during the on time period.

Most microcontrollers have at least one timer module, usually with a number of inputs and outputs. The inputs allow the timer to be used to measure the time of an input microconroller applied to the timer input, as illustrated below. In this example the rotating shaft produces a single pulse every revolution.

The microcontroller measures the time taken for a complete revolution and so determines the angular velocity of the shaft. The above figure illustrates how a timer output could be used to produce an output pulse train, possibly to drive some external logic. The timer is set up microcontroller that an on time and off time can be generated by the timer unit. The timer unit can also be used for generating a delay.

The timer is programmed with a specified count value which will be counted down decremented to zero. When the timer unit reaches zero a flag is set. This flag can be monitored by software so that the microcontroller will know when the timer unit has reached zero.

Since the time taken by the timer unit to decrement from the specified count value to zero is simply the count value multiplied by the time between decrement operations, a known delay period is produced. The time between decrement 681 is a function of the crystal clock oscillator frequency so it can be defined very accurately. The microcontroller can be doing other things between monitoring the flag bit so this is less wasteful in processor time than the simple software delay.

Catalog | EM Microelectronic

We will look at these aspects in more detail later on in the course. Just prior to turning on the LED, the timer unit is loaded with a count value the actual value being dictated by the delay time required. In due course the timer unit count value will reach zero, at which point a flag bit will be set. The time taken for the timer unit to decrement the count value to zero will be the time that the LED is on. Another way of using the timer to create a delay is to cause mjcrocontroller timer unit to interrupt the CPU when microdontroller timer reaches zero.

This can be more efficient in processor time since the microcontroller can be doing other things uninterrupted until the timer mjcrocontroller zero. The concept of interrupts will be miccrocontroller upon later in the course. This can be a very convenient way of transmitting data between two devices.


A disadvantage can be the slower speed of data transfer that a serial port has over a byte wide parallel data port.

The transfer rate can be programmed from within a range of typically baud bits per second to baud. The UART has additional signals that allow it to be connected to a modem. This should be borne in mind when considering microcomputer applications that require the use of a modem. Most SCI units can work in asynchronous mode, whilst some also support synchronous working. In the above 6182 we see a microcontroller with a SCI unit connected to another system which could be a PC via the transmit and receive pair.

This has not been 68112 in the above diagram. In some applications, a special purpose interface might be designed with its own serial interface.

Basic Computer Structure and the 6812 (Microcontrollers)

In the above diagram we see a remote display system controlled by a microcontroller via its SCI unit. For example, we might need to monitor log analogue signals from a strain gauge, or from a transducer converting temperature to an electrical analogue signal temperature transducer. Since microcontrollers are sometimes required for these types of applications, some are fitted with an Analogue to Digital Converter ADC. In most cases, the ADC is of the Successive Approximation type and there are a number of analogue channels between 4 and 8 is most common.

That is to say they are multiplexed with the digital ports and the decision to select whether the chip pins are to be used for analogue channel inputs or digital ports is made in software during the initial configuration of the program on reset. More on this later. It is uncommon for an ADC to derive more than 10 bits. For more demanding applications the ADC performance needs careful examination.

On chip sample and hold to accommodate ac signal sampling. Control over the sample clock and synchronisation between channels. CPU loading at higher sampling frequencies. Control over the sample clock allows the system to sample at a rate required by some applications which may be performing algorithms that require a specific sampling frequency for meaningful data calculations.

Higher clocking speeds means less time to do things. In general, most 8 bit microcontrollers have limited performance due to the limited ADC resolution and CPU performance. They are restricted to simple data logging and measurement applications not requiring high precision. Most 8 bit microcontrollers are unable to perform complex calculations owing to their limited instruction set and speed. For more intensive applications involving complex algorithms, a DSP is a better choice. A simple typical application is illustrated below.

Here we see a microcontroller being used to measure an analogue signal level. The microcontroller includes an ADC module and one of its digital input ports has been configured by software to be an analogue input channel.

The software running on the microcontroller will perform an Analogue to Digital conversion of the input signal, then determine whether the input signal is above or below some pre-defined limit. It will then turn on the appropriate LED. We have now covered most of the units found in a microcontroller.

Note that not all microcontrollers will contain all of these units. Most manufacturers of microcontroller chips produce a range or family of microcontroller devices. The same interface can be used to connect two microcontrollers together so that they can pass data between each other. This can allow a number of microcontrollers in a system to share data or allow one microcontroller the master to control a number of other microcontrollers the slaves.

This has become particularly important since the wiring loom in an microconfroller can now account for a substantial proportion of the vehicle weight. Serial data following a pre-defined protocol is transmitted around a number of sub-system units which also contain CAN interfacing units.


The CAN interface is used to control such things as the operation of the lights, monitor the engine parameters, even control the braking system, using a distributed CAN bus twin wire pair. The heavy wiring can therefore be kept short and only a power distribution system is required to get power to the individual unit being controlled. Each device to be controlled and each device sending data to another part of the automobile contains a CAN interface device.

Each CAN interface is called a node. Data messages transmitted from any node on a CAN bus do not contain addresses of either the transmitting node or of any intended receiving node. Instead, an identifier that is unique throughout the network labels the content of the message eg. All other nodes on the network receive the message and each performs an acceptance test on the identifier to determine if the message and hence its content is relevant to that particular node.

Some of the more prominent names manufacturing microcontroller chips have introduced CAN units into their range of microcontrollers. Study Task 1 Visit the Microchip web site and look at the range of microcontrollers that they provide. These microcontrollers are collectively called PIC microcontrollers, meaning that they are P eripheral I nterface C ontrollers. This will give you a feel for the support provided by the particular microcontroller manufacturer.

Study Task 2 Look at the following web sites: What are the main reasons for having a timer module on a microcontroller? The microcontroller can execute instructions in microseconds. External operations usually need to occur at very much reduced rates. What is the typical resolution for an Analogue to Digital Converter in the microcontroller devices you have seen? There are a few with 10 bit ADCs, but these are still relatively rare.

Some microcontrollers have a serial port. Could this serial port be used to connect to an external modem? The serial ports available on most microcontrollers do not allow a modem to be connected to the serial port. This means that an application requiring a modem will need to use an external serial port such as a UART to connect to the modem device. Give some examples of microcontrollers that you have come across that contain a serial peripheral port. Are there any external devices that could be used with these ports?

After looking at the Motorola web site, what are the differences between the and microcontroller devices in terms of the number and type of peripheral devices they contain? Both the and the contain a very wide range of peripheral devices. What is the maximum amount of external memory that can be connected to the microcontroller? Can this external memory be used for either program or data memory? The address bus is 16 bits wide so it can handle up to 2 16 memory locations.

The total amount of external memory is therefore – the memory available on the microcontroller chip itself. What are the main differences between the and microcontroller architectures? Essentially, the is an eight bit microcontroller having an 8 bit data bus width whilst the is a sixteen bit microcontroller having a 16 bit data bus.

Both microcontrollers share the same basic architecture and instruction set. This does not mean that a program designed to run on a will run on a What are the main features of the Intel 87C range of microcontrollers? What type of application have Intel targeted this microcontroller towards?