The 74HC; 74HCT is an 8-bit D-type transparent latch with 3-state outputs . The device features latch enable (LE) and output enable. The 74HC; 74HCT is a high-speed Si-gate CMOS device and is pin The 74HC; 74HCT has octal D-type transparent latches. The MM74HCT octal D-type latches and. MM74HCT octal D-type flip-flop advanced silicon-gate. CMOS technology, which provides the inherent benefits.
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74HC/HCT Octal D-type transparent latch;. 3-state. For a complete data sheet, please also download: • The IC06 74HC/HCT/HCU/HCMOS. The 74HC; 74HCT is a high-speed Si-gate CMOS device and is pin The 74HC; 74HCT has octal D-type transparent latches featuring separate. The MC74HCTA is identical in pinout to the LS This device be used as a level converter for interfacing TTL or NMOS outputs to. High–Speed CMOS.
IEC DM IEC 74LS DM 74LS All the parts are packaged for through hole PCB layout, but there are no simulator models. DM 74ALS DM 74S IEC 74S51 74S IEC 74S IEC 74S15 74S DM 74S64 74S 74S DM 74S03 74S IEC 74S85 74S DM 74S86 74S 74S DM 74S 74S 74S IEC 74S 74S IEC 74S40 74S All the parts are packaged for through hole PCB layout but there are no simulator models.
Contents 74F00 74F DM 74F IEC 74F The abilities of this circuit are expressed in the "instruction set" which is different for each microcontroller family. It is a kind of working desk used for storing all data upon which some operations should be executed addition, shift etc.
It also stores the results ready for use in further processing. One of the SFRs, called the Status Register, is closely related to the accumulator, showing at any given time the "status" of a number stored in the accumulator the number is greater or less than zero etc.
A bit is just a word invented to confuse novices at electronics. Joking aside, this word in practice indicates whether the voltage is present on a conductor or not. If it is present, the approprite pin is set to logic one 1 , i.
Otherwise, if the voltage is 0 V, the appropriate pin is cleared 0 , i. It is more complicated in theory where a bit is referred to as a binary digit, but even in this case, its value can be either 0 or 1. Each microcontroller has one or more registers called a port connected to the microcontroller pins. Because it is possible to change a pin function according to the user's needs.
These registers are the only registers in the microcontroller the state of which can be checked by voltmeter! Oscillator Even pulses generated by the oscillator enable harmonic and synchronous operation of all circuits within the microcontroller. It is usually configured as to use quartz-crystal or ceramics resonator for frequency stabilization. It can also operate without elements for frequency stabilization like RC oscillator. It is important to say that program instructions are not executed at the rate imposed by the oscillator itself, but several times slower.
It happens because each instruction is executed in several steps. For some microcontrollers, the same number of cycles is needed to execute any instruction, while it's different for other microcontrollers. Accordingly, if the system uses quartz crystal with a frequency of 20MHz, the execution time of an instruction is not expected 50nS, but , or even nS, depending on the type of the microcontroller!
These are commonly 8- or bit SFRs the contents of which is automatically incremented by each coming pulse. Once the register is completely loaded, an interrupt is generated!
If these registers use an internal quartz oscillator as a clock source, then it is possible to measure the time between two events if the register value is T1 at the moment measurement has started, and T2 at the moment it has finished, then the elapsed time is equal to the result of subtraction T2-T1. If the registers use pulses coming from external source, then such a timer is turned into a counter.
This is only a simple explanation of the operation itself. A register or a memory cell is an electronic circuit which can memorize the state of one byte. Besides 8 bits available to the user, each register has also a number of addressing bits. It is important to remember that: All registers of ROM as well as those of RAM referred to as general-purpose registers are mutually equal and nameless.
During programming, each of them can be assigned a name, which makes the whole operation much easier. All SFRs are assigned names which are different for different types of the microcontrollers and each of them has a special function as their name suggests.
Watchdog timer The Watchdog Timer is a timer connected to a completely separate RC oscillator within the microcontroller. If the watchdog timer is enabled, every time it counts up to the program end, the microcontroller reset occurs and program execution starts from the first instruction. The point is to prevent this from happening by using a special command.
The whole idea is based on the fact that every program is executed in several longer or shorter loops. If instructions resetting the watchdog timer are set at the appropriate program locations, besides commands being regularly executed, then the operation of the watchdog timer will not affect the program execution.
Reset occurs! Power Supply Circuit There are two things worth attention concerning the microcontroller power supply circuit: Brown out is a potentially dangerous state which occurs at the moment the microcontroller is being turned off or when power supply voltage drops to the lowest level due to electric noise. As the microcontroller consists of several circuits which have different operating voltage levels, this can cause its out of control performance.
In order to prevent it, the microcontroller usually has a circuit for brown out reset built-in. This circuit immediately resets the whole electronics when the voltage level drops below the lower limit. Reset pin is usually referred to as Master Clear Reset MCLR and serves for external reset of the microcontroller by applying logic zero 0 or one 1 depending on the type of the microcontroller. In case the brown out is not built in the microcontroller, a simple external circuit for brown out reset can be connected to this pin.
However, in other cases, when it is necessary to establish communication between two devices on longer distances it is obviously not possible to use parallel connections.
Then, serial communication is the best solution. Today, most microcontrollers have several different systems for serial communication built in as a standard equipment. Which of them will be used depends on many factors of which the most important are: How many devices the microcontroller has to exchange data with?
How fast the data exchange has to be? What is the distance between devices? Is it necessary to send and receive data simultaneously? One of the most important things concerning serial communication is the Protocol which should be strictly observed. It is a set of rules which must be applied in order that devices can correctly interpret data they mutually exchange.
A byte consists of 8 bits grouped together. If a bit is a digit then it is logical that bytes are numbers. All mathematical operations can be performed upon them, just like upon common decimal numbers, which is carried out in the ALU.
It is important to remember that byte digits are not of equal significance. The largest value has the leftmost bit called the most significant bit MSB.
The rightmost bit has the least value and is therefore called the least significant bit LSB. Since 8 digits zeros and ones of one byte can be combined in different ways, the largest decimal number which can be represented by one byte is one combination represents zero.
Program Unlike other integrated circuits which only need to be connected to other components and turn the power supply on, the microcontrollers need to be programmed first. This is a so called "bitter pill" and the main reason why hardware-oriented electronics engineers stay away from microcontrollers.
It is a trap causing huge losses because the process of programming the microcontroller is basically very simple. In order to write a program for the microcontroller, several "low-level" programming languages can be used such as Assembly, C and Basic and their versions as well. Writing program procedure consists of simple writing instructions in the order in which they should be executed.
There are also many programs running in Windows environment used to facilitate the work providing additional visual tools.
This book describes the use of Assembly because it is the simplest language with the fastest execution allowing entire control on what is going on in the circuit. Interrupt - electronics is usually more faster than physical processes it should keep under control.
This is why the microcontroller spends most of its time waiting for something to happen or execute. In other words, when some event takes place, the microcontroller does something.
In order to prevent the microcontroller from spending most of its time endlessly checking for logic state on input pins and registers, an interrupt is generated. It is the signal which informs the central processor that something attention worthy has happened. As its name suggests, it interrupts regular program execution.
It can be generated by different sources so when it occurs, the microcontroller immediately stops operation and checks for the cause. If it is needed to perform some operations, a current state of the program counter is pushed onto the Stack and the appropriate program is executed.
It's the so called interrupt routine. Stack is a part of RAM used for storing the current state of the program counter address when an interrupt occurs. In this way, after a subroutine or an interrupt execution, the microcontroller knows from where to continue regular program execution.
This address is cleared after returning to the program because there is no need to save it any longer, and one location of the stack is automatically availale for further use. In addition, the stack can consist of several levels.
Chapter 2 : Microcontroller Architecture 2. What is all this about? The whole story has its beginnings in the far 80s when Intel launched the first series of microcontrollers called the MCS Even though these microcontrollers had quite modest features in comparison to the new ones, they conquered the world very soon and became a standard for what nowadays is called the microcontroller.
The main reason for their great success and popularity is a skillfully chosen configuration which satisfies different needs of a large number of users allowing at the same time constant expansions refers to the new types of microcontrollers.
This is the reason for having a great number of various microcontrollers which basically are solely upgraded versions of the family.
What makes this microcontroller so special and universal so that almost all manufacturers all over the world manufacture it today under different name? As seen in figure above, the microcontroller has nothing impressive in appearance: 4 Kb of ROM is not much at all.
The whole configuration is obviously thought of as to satisfy the needs of most programmers working on development of automation devices. One of its advantages is that nothing is missing and nothing is too much. Pin 9: RS A logic one on this pin disables the microcontroller and clears the contents of most registers. In other words, the positive voltage on this pin resets the microcontroller. By applying logic zero to this pin, the program starts execution from the beginning.
Pins Port 3 Similar to port 1, each of these pins can serve as general input or output. Besides, all of them have alternative functions: Pin RXD Serial asynchronous communication input or Serial synchronous communication output. Pin TXD Serial asynchronous communication output or Serial synchronous communication clock output. Pin INT0 Interrupt 0 input.
Pin INT1 Interrupt 1 input.