Name the most unusual application of a microcontroller that you have seen actually for sale. Name the most likely bit size for each of the following products. Explain why ROMless versions of microcontrollers exist. Name two ways to speed up digital data processing. List three essential items needed to make up a development system for programming microcontrollers. Search the literature and determine whether any manufacturer has announced a bit microcontroller.
The features of the computer are best learned by studying the internal hardware design, also called the architecture of the device, to determine the type, number, and size of the registers and other circuitry. The hardware is manipulated by an accompanying set of program instructions.
Once familiar with the hardware and software. This chapter provides a broad overview of the architecture of the l. An enhanced version of the , the , also exists with its own family of variations and even includes one member that can be programmed in BASIC. This gal- axy of parts. The block diagram of the i in Figure 2.
These registers and memory locations can be made to operate using the software instructions that are incorporated as part of the design.
8051 Microcontroller : Architecture, Programming and Applications
The program instructions have to do with the control of the registers and digital data paths that are physically contained inside the i , as well as memory locations that are physically located outside the i. The model is complicated by the number of special—purpose registers that must be present to make a microcomputer a microcontroller. Others, which are generally indis- tinguishable from each other, are grouped in a larger block, such as internal ROM or RAM memory.
Each register, with the exception of the program counter, has an internal l-byte ad- dress assigned to it. That is, the entire byte of data at such register addresses may be read or altered, or individual bits may be read or altered. Software instructions are gener- ally able to specify a register by its address, its symbolic name, or both. A pinout of the i packaged in a pin DIP is shown in Figure 2. For this reason. A15 P2. Pin num- bers and pin names are shown inside the DIP package. Not all of the possible l features may be used at the same time. Programming instructions or physical pin connections determine the use of any multi- function pins.
For example, port 3 bit 0 abbreviated P3. The system designer decides which of these two functions is to be used and designs the hard- ware and software alfecting that pin accordingly. The Oscillator and Clock The heart of the i is the circuitry that generates the clock pulses by which all internal operations are synchronized. The crystal frequency is the basic internal clock fre- quency of the microcontroller. Minimum frequencies imply that some internal memories are dynamic and must always operate above a minimum frequency, or data will be lost.
Communication needs often dictate the frequency of the oscillator due to the require- ment that internal counters must divide the basic clock rate to yield standard communica- tion bit per second baud rates. How- ever, decreases in frequency stability and accuracy make the ceramic resonator a poor choice if high-speed serial data communication with other systems, or critical timing, is to be done. The oscillator formed by the crystal, capacitors, and an on-chip inverter generates a pulse train at the frequency of the crystal, as shown in Figure 2.
The clock frequency, f. The smallest interval of time to accomplish any simple instruction, or part of a complex instruction, however, is the machine cycle. The machine cycle is itself made up of six states. A state is the basic time interval for discrete operations of the microcontroller such as fetching an opcode byte, decoding an opcode, executing an opcode, or writing a data byte. Program instructions may require one, two, or four machine cycles to be executed, depending on the type of instruction. A 12 megahertz crystal yields the con- venient time of one microsecond per cycle.
An I LO megahertz crystal, while seem- ingly an odd value, yields a cycle frequency of 92l. Each is used to hold the address of a byte in memory. Program instruction bytes are fetched from locations in memory that are addressed by the PC. The PC is automatically incremented after every instruction byte is fetched and may also be altered by certain instructions. The PC is the only register that does not have an internal address. Two of these, registers A and B, comprise the mathematical core of the central processing unit CPU. The A register is also used for all data transfers be- tween the ] and any external memory.
The B register is used with the A register for multiplication and division operations and has no other function other than as a location where data may be stored. The ! The program status word is shown in Figure 2. Internal Memory A functioning computer must have memory for program code bytes, commonly in ROM, and RAM memory for variable data that can be altered as the program runs. Additional memory can be added externally using suitable circuits. Unlike microcontrollers with Von Neumann architectures, which can use a single memory address for either program code or data, but norfor both.
In- ternal circuitry accesses the correct memory based upon the nature of the operation in progress. Thirty-two bytes from address 00h to lFh that make up 32 working registers or- ganized as four banks of eight registers each. The four register banks are num- bered 0 to 3 and are made up of eight registers named R0 to R7. Each register can be addressed by name when its bank is selected or by its RAM address. Thus R0 of bank 3 is R0 if bank 3 is currently selected or address l8h whether bank 3 is selected or not. Bits R50 and RS1 in the PSW determine which bank of registers is currently in use at any time when the program is mnning.
Register banks not selected can be used as general-purpose RAM. Bank 0 is selected upon reset. Thus, for example. Ad- dressable bits are useful when the program need only remember a binary event switch on, light off, etc.
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Internal RAM is in short supply as it is, so why use a byte when a bit will do? A general-purpose RAM area above the bit area. The Stack and the Stack Pointer The stack refers to an area of internal RAM that is used in conjunction with certain op- codes to store and retrieve data quickly. When data is to be placed on the stack, the SP increments before storing data on the stack so that the stack grows up as data is stored. As data is retrieved from the stack, the byte is read from the stack, and then the SP decrements to point to the next available byte of stored data. Operation of the stack and the SP is shown in Figure 2.
The SP is set to 07h when the is reset and can be changed to any intemal RAM address by the programmer.
The stack is limited in height to the size of the internal RAM. The stack has the poten- tial if the programmer is not careful to limit its growth to overwrite valuable data in the register banks, bit-addressable RAM. The stack is normally placed high in internal RAM. This feature allows the programmer to change only what needs to be altered, leaving the remaining bits in that SFR unchanged.
8051 Microcontroller Architecture, Programming and Application
In Figure 2. SFRs are named in certain opcodes by their functional names, such as A or THO, and are referenced by other opcodes by their addresses, such as 0E0h or 8Ch. Note that any address used in the program must start with a number; thus address E0h for the A SFR begins with 0. Failure to use this number convention will result in an assembler error when the program is assembled. Internal ROM The ] is organized so that data memory and program code memory can be in two entirely different physical memory entities.
Each has the same address ranges.testswarmsrv01.coex.cz/sepox-best-mobile-tracker.php
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The structure of the internal RAM has been discussed previously. A corresponding block of internal program code. Code bytes can also be fetched exclusively from an external memory, addresses h to FFFFh. As noted in Chapter 1, microprocessor designs must add additional chips to interface with external circuitry; this ability is built into the microcontroller. To be commercially viable, the i had to incorporate as many functions as were technically and economically feasible. The main constraint that limits numerous functions is the number of pins available to the !
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