Microprocessor Operation

h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 1 Chapter 1 Microprocessor Operation This chapter lets you understand that the microprocessor is built of a CPU, memory and data input/output ICs, that it operates on a "stored program" basis, and that it is available in multi-chip/single-chip architectures. These concepts are not confined to the H8/300H but extend to all other kinds of microprocessors. 1.1 Microprocessor Configuration The microprocessor is said to be a "computer built around ICs." Mainframes, minis, and microprocessors all share the same principles of operation and vary only in their scale, speed and architecture. The minimum components required to build a computer are the CPU, memory and I/O devices as shown in Figure 1.1. Figure 1.1 Microprocessor configuration All these components of a microprocessor are fabricated of a single IC. Such ICs are coupled to build a computer. Three minimum ICs needed to make up a microprocessor are the CPU, memory, and peripheral IC. h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 2 CPU (Central Processing Unit) The CPU forms the nucleus of any computer by executing instructions. Microprocessors are grouped into 4-bit, 8-bit, 16-bit, and 32-bit microprocessors according to the length of bits they can handle at a time. A 4- bit microprocessor can handle four binary digits in a single instance of calculation, but as many as eight digits in two instances and 16 in four instances. The microprocessor is also known as a "MPU (microprocessing unit)", "microprocessor", or simply "processor." Memory (Memory) A device on which instructions and data are stored. Without memory, programs and data cannot be used. In a microprocessor, ROM (read-only memory) and RAM (random access memory) are used. Input device (Input) A data input device. The keyboard and mouse of a PC, for example, are data input devices. With a built-in controller, switches and sensors are input devices. These input devices cannot be directly connected to a CPU, but they must be attached to the CPU by way of a "peripheral IC," containing connection circuitry. Depending on the kind of input device to be connected to the CPU, an appropriate peripheral IC is used. Output device (Output) A data output device. The display and printer of a PC, for example, are data output devices. With a built-in controller, display LEDs, motors, heaters and so on are output devices. Like input devices, output devices are attached to a CPU by way of a "peripheral IC." Depending on the kind of output device to be connected to the CPU, an appropriate peripheral IC is used. Input devices and output devices are collectively called "peripherals." 1.2 Stored Program Computers The stored program computer provides a most precise concept of the operating principles of a computer. It might be safely said that "All modern computers are stored program computers." The stored program computer was first conceptualized in 1947 by John von Neumann and is also known as a "Neumann computer." In the stored program computer, the CPU reads instructions stored in memory in sequence, decodes and executes them. The act of the CPU reading an instruction from memory is called "fetch." Interpreting the fetched instruction to see what operation it defines is called "decode." The CPU then proceeds to perform, or "execute," the operation defined by the instruction. When the CPU has finished executing the h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 3 instruction, it fetches the next instruction. After all, the CPU infinitely repeats the following cycle of operations: - Instruction fetch - Instruction decoding - Instruction execution Any microprocessor has a program counter in its CPU. The program counter always holds the "address of the next instruction to be executed." When the CPU reads an instruction, the program is automatically updated to indicate the address of the next instruction in sequence. The program counter thus ensures that instructions stored in memory will be executed in correct sequence. Figure 1.2 Operating principles of a stored program computer 1.3 Memory Memory devices are broadly classified into two categories: ROM (read- only memory) and RAM (random access memory). You can only read stored data from ROM but cannot write to it. Stored data is preserved intact, however, when the microprocessor is switched off. Use ROM to store valuable data that needs to be protected from erasure in times of power failures, typically, programs. Instructions are stored in ROM. Each meaningful collection of instructions is a program. Any microprocessor would be inoperable unless it comes up with "programs available for ready use" when switched on. ROM fills this need. Data can be written to and read from RAM as desired. Stored data would be lost, however, once the microprocessor is switched off. Even when h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 4 the microprocessor is switched on again, previous data is no longer left. Hence, RAM is used as temporary data storage. Programs may also be placed in RAM, but will be lost once the microprocessor is switched off. To run programs in RAM, it is necessary to attach an external storage device, such as a floppy disk or hard disk drive, and transfer the programs to RAM from external storage to RAM when the microprocessor is switched on. Mask ROM (Mask ROM) When a memory IC is manufactured in the factory, programs are written to it. A mask is a plate of glass imprinted with patterns of wirings and transistors used in the IC manufacturing process. Users have a semiconductor manufacture custom-build a mask to manufacture a memory IC. Advantages - Suitable for volume production - Low cost Disadvantages - Long lead-time from ordering to completion - Not reprogrammable once built EPROM (Erasable & Programmable ROM) Stored data can be erased by ultraviolet irradiation. To this end, a special package with a glass window is used. An EPROM writer is used to write to EPROM. EPROM is erasable and programmable about 100 times. Advantage - Erasable and programmable and thus convenient for testing and debugging Disadvantage - Expensive because of the use of a special package OTPROM (One Time Programmable ROM) An EPROM chip housed in an inexpensive plastic package. Stored data cannot be erased by ultraviolet irradiation because no glass window can be attached to the plastic package. OPTROM can be written only once, but it comes by far cheaper than EPROM. Programs are debugged in EPPROM and, when finalized, moved to OTPROM for volume production. Advantage - Cheaper than EPROM and suitable for small-batch production Disadvantage - Not erasable and programmable EEPROM (Electrically Erasable & Programmable ROM) EEPROM can be electrically erased and programmable, and can be reprogrammed when mounted on a board as a finished product. EEPROM is reprogrammable about tens of thousand times. h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 5 Advantages - Onboard reprogrammable - Ready for infinite times of reprogramming Disadvantage - Expensive Flash memory (Flash Memory) A variation of flash memory, which is cheaper and larger-sized. Advantage - Cheaper and larger-sized than EEPROM Disadvantages - Unable to write address by address, unlike EEPROM - Memory IC divided into blocks for erasure and reprogramming block by block Static RAM (Static RAM) RAM with its storage circuit built of flip-flops. Given a supply voltage, static RAM preserves stored data intact. It dissipates least power when out of use. Because six transistors are used to build its flip-flops, static RAM offers less storage capacity than does ROM. Advantages - Fast - Low power consumption and suitable for battery backup Disadvantages - Expensive - Small storage capacity Dynamic RAM (Dynamic RAM) Simplified storage circuitry with only one capacitor and one transistor to provide each bit of memory, and hence larger-sized than static RAM. Charges on the capacitors, however, drain with time, resulting ultimately in loss of stored data. Before such loss, all stored data must be read out and refreshed. Power alone does not allow dynamic RAM to retain stored data but requires refreshing for that purpose. Advantage - Cheap and large-sized Disadvantage - Refreshing required Table 1.1 summarizes features of key ROM and RAM devices. h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 6 Table 1.1 Kinds and features of memory devices Kind Features ROM Mask ROM Large-sized, cheap, volume production use, custom fabrication, not reprogrammable EPROM Programmable and erasable by ultraviolet irradiation. Testing, debugging OTPROM Low-volume production use, one-time programmable EEPROM Electrically programmable, onboard reprogrammable Flash memory Electrically erasable and programmable, cheaper and larger sized than EEPROM RAM Static RAM Stored data preserved under voltage input alone, fast, battery backup use Dynamic RAM Refreshing required to preserve data, large-sized, cheap 1.4 Single-Chip/Multi-Chip Microprocessors Putting a CPU, ROM, RAM, and data input/output circuitry into a single IC will make a single-chip microprocessor. Single-chip microprocessors come compact and cheap, but do not allow users to choose built-in functions at their option. Single-chip microprocessors are also known as "microcomputer units (MCUs)," because they are made of a single IC. On the other hand, a computer fabricated from a mix of a CPU, memory and data input/output devices is called a "multi-chip microprocessor." Multi-chip microprocessors offer users greater freedom in their component choice. Multi- chip microprocessors will prove more advantageous for larger systems involving complexities of input/output. See how a single-chip microprocessor and a multi-chip microprocessor differ in Figure 1.3. h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 7 Figure 1.3 Single-chip microprocessor and multi-chip microprocessor Single-chip microprocessors are used as built-in controllers. When a single-chip microprocessor is switched on, the control program stored in its internal ROM launches instantly. Internal RAM is used as temporary storage. The internal data input/output circuits, too, have been chosen to support the single-chip microprocessor as s controller. Kinds of internal ROM Early single-chip microprocessors included only mask ROM and were available only for use in mass-produced products. Subsequently EPROM has made inroads into single-chip microprocessors as internal ROM. As testing and debugging was carried out in erasable and programmable packages with windows and inexpensive plastic- packaged OTPROM used on commercialization, single-chip microprocessors came to be used in products manufactured in small batches as well. Now, single-chip microprocessors with internal EEPROM and flash memory are available for use in various applications. As the IC manufacturing technology has been advancing from year to year, with continuing increases in the sizes of internal ROM and RAM, state-of-the-art data input/output functions have been used in single-chip microprocessors in an expanding of applications. Microprocessors and memory A memory device organized into 8 bits per address is used. Each sequence of 8 bits is called a "byte," and memory sizes are stated in the unit byte. 64K bytes of memory could be connected to classical 8-bit microprocessors as standard. This memory size indicates 8 bits per address in a memory space of 64K (65536 addresses). Eight bits of memory per address are h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 8 also connected to 16- and 32-bit microprocessors, as well as 8-bit microprocessors. 1. What are the three key ICs needed to make up a microprocessor? (CPU (MPU ) ) (Memory ) (Peripheral IC) Mainframes and minis share the same computer architecture. Microprocessors are characterized by the fact that three components of the computer - namely, the CPU, memory, and input/output circuit (peripheral IC) - are each fabricated as an IC. 2. Fill the blanks with appropriate words or phrases. The (stored program computer) provides a most precise concept of the operating principles of a computer. This was first conceptualized in 1947 by (John von Neumann). The stored program computer materializes the principles of a computer in which the CPU reads instructions from memory and executes them. This is also known as a "Neumann computer," because of its conceptualization by John von Neumann. 3. Mention one advantage and one disadvantage for each of the following kinds of memory: Mask ROM Advantage (Inexpensive, large-sized ) Disadvantage (Available only on order, not reprogrammable) EPROM Advantage (Erasable and programmable) Disadvantage (Expensive ) Dynamic RAM Advantage (Inexpensive, large-sized ) Disadvantage (Refreshing required ) Mask ROM is volume-produced at factory at low cost, and features circuit simplicity, offering large-sized memory. Mask ROM can be manufactured only by order and is not reprogrammable after it is built. EPROM allows about 100 times of erasure and reprogramming using a special writer, but the special package with a glass window adds to its cost. Using capacitors as storage devices, DRAM is simple in circuitry, inexpensive, and large-sized, but what is inconvenient, it must be refreshed so that charges on the capacitors do not drain. h t t p : / / r e s o u r c e . r e n e s a s . c o m Page 9 4. Mention one advantage and one disadvantage for the microprocessor. Advantage (Compact, inexpensive ) Disadvantage (Limited internal functionality ) (Small memory size Not suitable for use in larger systems ) A single-chip microprocessor has all functions assembled on a single chip and therefore comes compact and more inexpensive than purchasing its components separately. Its scale of integration is limited and is not suitable for mounting extra-large-sized memory. . of microprocessors. 1.1 Microprocessor Configuration The microprocessor is said to be a "computer built around ICs." Mainframes, minis, and microprocessors. Single-chip microprocessor and multi-chip microprocessor Single-chip microprocessors are used as built-in controllers. When a single-chip microprocessor