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The Microprocessor-based The Microprocessor-based PC SystemPC System

Microprocessor CourseElectrical Engineering Department

University of Indonesia

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Bus, Memory & I/O Section

• Fig. 1.2 shows the general block diagram of the PC

• A bus is a set of common connections that carry the same type of information

• The memory system is divided into three main parts: TPA, system area, XMS (optional)

• The pentium Pro-based computer system, for example, can have up to 1M less than 4G or 64G of extended memory (Fig. 1.3)

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Bus, Memory & I/O Section (cont’d)

• The Transient Program Area (TPA) holds the OS and other program that control the computer system

• It also stores any currently active or inactive application programs

• The length of TPA is 640 KB

• The memory map (fig. 1.4), hexadecimal addr.) shows how many areas of the TPA are used for system programs, data, and drivers

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Bus, Memory & I/O Section (cont’d)

• The interrupt vectors access various features of the DOS, BIOS (Basic I/O System), and application

• The BIOS and DOS communications areas contain transient data used by program to access I/O devices and internal features of the computer system

• The IO.SYS is a program that loads into the TPA from the disk whenever an MSDOS or PC DOS system is started

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Bus, Memory & I/O Section (cont’d)

• The MSDOS (PCDOS) program occupies two areas of memory

• The size of the driver area and # of drivers change from one computer to another

• The COMMAND.COM program controls the operation of the computer from the keyboard

• The free TPA area holds application prog-rams as they are executed

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Bus, Memory & I/O Section (cont’d)

• The system area (Fig. 1.5) contains program on either a read-only memory or flash memory and also areas of read/write (RAM) memory for data storage

• The area at locations C8000H-DFFFFH is often open or free. It is usually used for the Expanded Memory System (EMS) -> Fig.1.6

• The EMS allows a 64 KB page frame of memory to be used by application programs

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Bus, Memory & I/O Section (cont’d)

• The input/output space extends from I/O port 0000H to port FFFFH.

• An I/O port is similar to a memory address but addresses an I/O device

• The I/O area contains two major sections (Fig 1.7):– the area below I/O location 0500H is reserved for

system devices– the remaining area is available I/O space for

expansion

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The MicroprocessorThe Microprocessor

• The microprocessor is the controlling element in a computer system and is sometimes referred to as the CPU (Central Processing Unit)

• Memory and I/O are controlled through instructions that are stored in the memory and executed by the microprocessor

• The microprocessor performs three main tasks for the computer system:

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The Microprocessor (cont’d)The Microprocessor (cont’d)

– Data transfer between itself and the memory or I/O systems

– simple arithmetic & logic operations (Table 1.3)– program flow via simple decisions

• Why the microprocessor is powerful?– Able to execute millions of instructions per

second from a program or software (group of instructions) stored in the memory system

– able to make simple decision, based upon numerical facts (Table 1.4)

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BusesBuses

• The microprocessor controls memory and I/O through a series of connections called buses

• A bus is a common group of wires that interconnect components in a computer system

• Buses select an I/O or memory device, transfer data between an I/O device or memory and the microprocessor, and control the I/O and memory system

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BusesBuses

• Three buses exist for the transfer of information: address, data, control (Fig 1.8)

• The address bus requests a memory location from the memory or an I/O location from the I/O devices

• Table 1.5 depicts a complete listing of bus and memory sizes on the Intel family of p

• Figure 1.9 shows the memory width and sizes of 8086-80486 and Pentium p

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BusesBuses

• The memory sizes and organizations differ between various member of the Intel p familiy

• The control bus contains lines that select the memory or I/O and cause them to perform a read or write operation.

• Four control bus connections: MRDC, MWTC, IORC, IOWC

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BusesBuses

• The micro-instructions for READ:– the p reads the contain of memory location by

sending the memory an address through address bus

– the p sends the memory read control signal (MRDC) to cause memory to read data

– the data read from the memory are passed to the microprocessor through the data bus

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