The W registers are memory-mapped. The second form is more conventional, allowing three operands, which may be any of 16 W registers. The destination and one of the sources also support addressing modes, allowing the operand to be in memory pointed to by a W register. There is no distinction between memory space and register space because the RAM serves the job of both memory and registers, and the RAM is usually just referred to as the register file or simply as the registers. Special-purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series, and all PIC devices have some banking mechanism to extend addressing to additional memory.
Later series of devices feature move instructions, which can cover the whole addressable space, independent of the selected bank. In earlier devices, any register move had to be achieved through the accumulator. External data memory is not directly addressable except in some PIC18 devices with high pin count. In general, there is no provision for storing code in external memory due to the lack of an external memory interface.
All PICs handle and address data in 8-bit chunks. However, the unit of addressability of the code space is not generally the same as the data space. In contrast, in the PIC18 series, the program memory is addressed in 8-bit increments bytes , which differs from the instruction width of 16 bits. In order to be clear, the program memory capacity is usually stated in number of single-word instructions, rather than in bytes.
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PICs have a hardware call stack , which is used to save return addresses. The hardware stack is not software-accessible on earlier devices, but this changed with the 18 series devices. Hardware support for a general-purpose parameter stack was lacking in early series, but this greatly improved in the 18 series, making the 18 series architecture more friendly to high-level language compilers. The instruction set includes instructions to perform a variety of operations on registers directly, the accumulator and a literal constant or the accumulator and a register , as well as for conditional execution, and program branching.
Some operations, such as bit setting and testing, can be performed on any numbered register, but bi-operand arithmetic operations always involve W the accumulator , writing the result back to either W or the other operand register. To load a constant, it is necessary to load it into W before it can be moved into another register. On the older cores, all register moves needed to pass through W, but this changed on the "high-end" cores. PIC cores have skip instructions, which are used for conditional execution and branching. The skip instructions are "skip if bit set" and "skip if bit not set".
Because cores before PIC18 had only unconditional branch instructions, conditional jumps are implemented by a conditional skip with the opposite condition followed by an unconditional branch. Skips are also of utility for conditional execution of any immediate single following instruction. It is possible to skip instructions. The 18 series implemented shadow registers, registers which save several important registers during an interrupt, providing hardware support for automatically saving processor state when servicing interrupts.
The architectural decisions are directed at the maximization of speed-to-cost ratio. The PIC architecture was among the first scalar CPU designs [ citation needed ] and is still among the simplest and cheapest. The Harvard architecture, in which instructions and data come from separate sources, simplifies timing and microcircuit design greatly, and this benefits clock speed, price, and power consumption. The PIC instruction set is suited to implementation of fast lookup tables in the program space.
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Such lookups take one instruction and two instruction cycles. Many functions can be modeled in this way. Optimization is facilitated by the relatively large program space of the PIC e. Interrupt latency is constant at three instruction cycles. External interrupts have to be synchronized with the four-clock instruction cycle, otherwise there can be a one instruction cycle jitter. Internal interrupts are already synchronized.
PIC microcontrollers - Wikipedia
The constant interrupt latency allows PICs to achieve interrupt-driven low-jitter timing sequences. An example of this is a video sync pulse generator. This is no longer true in the newest PIC models, because they have a synchronous interrupt latency of three or four cycles. The following stack limitations have been addressed in the PIC18 series, but still apply to earlier cores:. With paged program memory, there are two page sizes to worry about: This register must be changed every time control transfers between pages.
Microchip will eventually phase out its older compilers, such as C18, and recommends using their XC series compilers for new designs. Judicious use of simple macros can increase the readability of PIC assembly language. It has macro instructions like mov b, a move the data from address a to address b and add b, a add data from address a to data in address b. It also hides the skip instructions by providing three-operand branch macro instructions, such as cjne a, b, dest compare a with b and jump to dest if they are not equal.
PIC microcontrollers
Within a series, there are still many device variants depending on what hardware resources the chip features:. Likewise, the original bit instruction set of the PIC and its direct descendants has been superseded by bit and bit instruction sets. UV erasable windowed versions of these chips can be ordered. Conversely, a C generally means it can only be erased by exposing the die to ultraviolet light which is only possible if a windowed package style is used. An L in the name indicates the part will run at a lower voltage, often with frequency limits imposed.
Free versions of the C compilers are also available with all features. But for the free versions, optimizations will be disabled after 60 days. It exists in numerous versions from a free demonstration to a more complete professional edition. Preview — Microcontroller Programming by Julio Sanchez. From cell phones and television remote controls to automobile engines and spacecraft, microcontrollers are everywhere.
Using the popular and pervasive mid-range 8-bit Microchip PIC R as an archetype, Microcontroller Programming offers a self-contained presentation of the multidisciplinary tools needed to design and implement modern embedded systems and microcontrollers. The authors begin with basic electronics, number systems, and data concepts followed by digital logic, arithmetic, conversions, circuits, and circuit components to build a firm background in the computer science and electronics fundamentals involved in programming microcontrollers.
For the remainder of the book, they focus on PIC architecture and programming tools and work systematically through programming various functions, modules, and devices. Helpful appendices supply the full mid-range PIC instruction set as well as additional programming solutions, a guide to resistor color codes, and a concise method for building custom circuit boards. Providing just the right mix of theory and practical guidance, Microcontroller Programming: The Microchip PIC R is the ideal tool for any amateur or professional designing and implementing stand-alone systems for a wide variety of applications.
Hardcover , pages. To see what your friends thought of this book, please sign up. To ask other readers questions about Microcontroller Programming , please sign up. Be the first to ask a question about Microcontroller Programming. Lists with This Book. An X-Bits microcontroller can manipulate data up to X bits in size. However, there are many MCUs that have a full instruction set that handles 8-Bit data alongside with a few ones for handling Bit words.
In this case, it should be called an 8-Bit machine! A specific microcontroller is considered as an X-Bit Computer if it has an instruction set that most of its instructions are designed to manipulate data words of X-Bits size. The 8-Bit microcontrollers are the most common with highest shipping volume in the market.
However, there are Bit and Bits microcontrollers that are used for high-performance applications that require excessive computational power. This represents the majority of the MCUs being manufactured nowadays. In the past, some chips had no program memory built-in and they had to connect it externally.
This type of MCUs had to disappear with the emergence of internal memory designs only 5 years later back in Some sophisticated functions could be achieved using the basic instructions available in the instruction set of a microprocessor. Here is an example of a set of assembly instructions that could be found in any device out there. And so on for the rest of the functions. Hence, there are basically two categories for instructions sets.
And there are devices with a bunch of sophisticated functions hardware-implemented with digital logic which have complex instruction sets. In conclusion, the 2 major computer architectures are the 2 listed down below. While the Harvard architecture had two separate memories. The diagram below shows you the difference between those two architectures. All in all, the Harvard architecture is the most common option for the microcontrollers used in embedded systems applications. Each company in the microcontrollers manufacturing business is producing different series families of their architecture.
The obvious reason for doing so is to satisfy the needs of many different segments that require microcontrollers chips with specific performance levels. These are the most common widely-available architectures out there. Or equivalently an 8-Bit AVR will do the job indeed. As the embedded industry is so broad and there is a room for every single architecture which at some point will be the best fit for the job. You will always be free to use the chip you want, there is no restriction to the 16FA chip.
In this case, please be advised to use my code listings at your own risk. Well, there are a few reasons to do so. I believe that platforms with very limited resources are the best choice to get started in embedded systems. Fewer instructions, less memory, less power, and less money. We are problem-solvers and optimizers. Having a platform with excessive resources contributes to growing bad coding habits that go forever uncorrected.
A Microcontroller is usually a black IC with a bunch of pins coming out of It. The most common package type used for prototyping is the DIP dual in-line which fits nicely in a typical breadboard. While the QFP packages are the most efficient ones, usually used for creating professional PCBs that take much less space.
You should also note that the external packaging material is a solid epoxy for protection purposes. But the actual microcontroller is actually much smaller. Here is a picture of a microcontroller chip internal structure. In which you can see that a typical microcontroller is something that is even smaller than the smallest of your nails!
Can you see those tiny wires coming out the core? We stated earlier that a microcontroller is just a smaller version of a full computer machine. Here is a brief table of the main components modules typically found in a generic microcontroller. The following hand-drawn diagram shows you the main components typically found in a generic microcontroller and how they are organized.
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With simplified interlinkings that connect all of these modules altogether. This is the working horse of the microcontroller internal system. It handles your program instructions and executes them after the processes of fetching and decoding. It also has the ALU inside which does all the arithmetic and logical calculations.
Microcontroller Programming: The Microchip PIC
A typical simple 8-Bit CPU will execute a single instruction in about 4 machine cycle. The Random Access Memory is the unit which contains the data registers which are used for data storage and also for controlling the operation of all other modules. The registers of the RAM could be categorized into two categories: Which are used to store data variables that will allocate random addresses.
Which are hard-wired to most of the modules within a microcontroller. This memory unit is dedicated to storing the program instructions assembly. Every single instruction is stored in an x-Bits register. The number of bits depends on the architecture and design of the CPU itself and its instruction set. Executing a full program is a matter of incrementing the PC that point to the instructions which will be executed by the CPU. You can input digital signal to a microcontroller with a simple push button or a sensor. Serial ports allow for advanced communication with a microcontroller.
As we can send or receive streams of data serially. This could be numbers, audio, images or even files. Serial ports are extensively used to create machine-machine interfaces as well as human-machine interfaces.
There is no embedded application that does something real in a real-world application that is not using a timer in one way or another. A typical microcontroller may have 1, 2 or more hardware timer modules. Which are mainly used for generating time intervals that separate specific events and control time-dependent events. An interrupt is an event that suspends the main program execution while the event is serviced Handled by another program.
Different microcontrollers have different interrupt sources which may include timers, serial ports, IRQs or even software interrupt. Immediately on receiving an interrupt signal, the current instruction is suspended, the interrupt source is then identified and the CPU branches vectors to an interrupt service routine stored in a specific address in memory. The interrupt handler program code is usually called interrupt service routine or ISR. The interrupt circuitry unit is a digital logic circuit that controls the generation of interrupt signals and commands the CPU to handle these interrupts requests on time.
These are basically the wires that connect everything inside a microcontroller. The bus is defined by its width, this feature is called bus width. The bus width is the number of the physical wires that make up the bus itself. It could be 4, 8, 16, or any number obviously. If a device A is connected to device B via a 4-wires bus, this could be symbolically represented as shown in the diagram below. The bus could be drawn as a straight line that connects a digital circuit to another. A microcontroller may or may not have any of the following modules.
It may have all of them as well.