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CSNB373: Microprocessor Systems

CSNB373: Microprocessor Systems. Chapter 6: Memory and I/O Interfacing. Intel 8086/8088 Pin-outs. Recall that Intel 8086/8088 are both 16-bit microprocessors with similar architecture. The only difference is that Intel 8086 has 16-bit data bus and Intel 8088 has 8-bit data bus.

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CSNB373: Microprocessor Systems

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  1. CSNB373: Microprocessor Systems Chapter 6: Memory and I/O Interfacing

  2. Intel 8086/8088 Pin-outs • Recall that Intel 8086/8088 are both 16-bit microprocessors with similar architecture. • The only difference is that Intel 8086 has 16-bit data bus and Intel 8088 has 8-bit data bus. • Both are packaged in 40-pin dual-in-line packages (DIPs). • The pin-out configuration can be slightly different depending on whether the processor is operating in minimum or maximum mode. • Maximum mode is used when the microprocessor is operating together with a co-processor.

  3. Intel 8086/8088 Pin-outs

  4. Intel 8086/8088 Pin-outs • For comparison, Intel Core-i7 microprocessors has more than 1000 pin-outs. • The actual pin-out configuration depends on the packaging used. • Example of packaging for Intel Core-i7 microprocessors: LGA775, LGA1366, LGA1156.

  5. Intel 8086/8088 Pin-outs • AD15 – AD0 • Address/data bus lines. • Contains memory address or I/O port number whenever ALE (Address Latch Enable) pin is 1. • Contains data whenever ALE is 0. • A19/S6 – A16/S3 • Address/status bus lines.

  6. Intel 8086/8088 Pin-outs • RD • Read signal. • When RD = 0, the data bus is receptive to data from memory or I/O devices. • READY • If READY = 0, the microprocessor enters into wait state and becomes idle. • Otherwise, the microprocessor functions normally.

  7. Intel 8086/8088 Pin-outs • INTR • Interrupt request. • If INTR = 1, the microprocessor enters an interrupt acknowledge cycle after the current instruction has completed execution. • NMI • Non-maskable interrupt. • Similar to INTR, except that interrupt will be executed even though the IF flag bit is 0. • Interrupt vector 2 will be used to service the interrupt.

  8. Intel 8086/8088 Pin-outs • INTA • Interrupt acknowledge. • Output a response when an interrupt signal is received on the INTR pin. • Upon receiving the response, the system circuit would then send the interrupt vector number on the data bus.

  9. Intel 8086/8088 Pin-outs • TEST • An input that is tested by the WAIT instruction. • If TEST = 0, the WAIT instruction functions as a NOP. • If TEST = 1, the WAIT instruction will wait for TEST to become 0. • This TEST pin is most often connected to the 8087 co-processor.

  10. Intel 8086/8088 Pin-outs • RESET • If RESET = 1 for four clocking periods, the microprocessor will reset itselt. • When the processor is reset, it executes instructions at memory location FFFF0H. • CLK • Connected to a clock to provide timing signal for the microprocessor.

  11. Intel 8086/8088 Pin-outs • VCC • Power supply input. • Provides +5.0 V, ±10 % signal to the microprocessor. • GND • Ground connection. • Intel 8086/8088 has two GND pins. • Both must be connected to ground for proper operation.

  12. Intel 8086/8088 Pin-outs • MN/MX • Minimum/maximum mode pin selection. • 0 – maximum, 1 – minimum. • BHE/S7 • Bus high enable pin. • BHE is set to 0 to enable the most-significant data bus bits (D15–D8) during a read or a write operation.

  13. Intel 8086/8088 Pin-outs • M/IO • Selects memory or I/O. • Indicates whether the address bus contains a memory address or an I/O port address. • 0 – I/O, 1 – memory. • WR • Write line. • Indicates whether the microprocessor is outputting data

  14. Intel 8086/8088 Pin-outs • DT/R • Data transmit/receive. • Shows whether the data bus is transmitting or receiving. • 1 – transmitting, 0 – receiving. • HOLD • Request a direct memory access (DMA). • HLDA • Indicates that the microprocessor has entered a HOLD state.

  15. Memory Pin Connections • Typical pins on a memory chip. • Address connection • Data connection • Selection input • Control input to select read or write operation.

  16. Memory Pin Connections • Address connections • To select memory location within the memory device. • The number of pins depend of the number of memory locations. • 1K (1024) – 10 pins • 1M (1048576) – 20 pins • 1G (1073741824) – 30 pins • 4G (4294967296) – 32 pins

  17. Memory Pin Connections • Data connections • Carries data to/from the memory device. • The number of pins is determined by the data width. • Most devices are currently 8-bit wide. • There are also devices with 16, 4 or 1 bit wide. • Catalog listings of memory devices often refer to memory locations times bits per location. • 1K x 8 means 1K memory locations and 8-bit in each location.

  18. Memory Pin Connections • Selection connection • An input which enables the memory device. • The memory device needs to be enabled in order for read or write operation to be performed. • Control connections • Used to choose whether a read or write operation is to be performed.

  19. Memory Interfacing • Intel 8088 has 8-bit data bus. • But later Intel microprocessors have 32-bit or even 64-bit data bus. • Does that mean modern memory devices have 32-bit or 64-bit wide data connection? • NO. • Most modern memory devices still have 8-bit wide data connection. • But what happen to the remaining data pins?

  20. Memory Interfacing • Processors with more than 8-bit wide data bus can use a number of memory banks. • For example, a microprocessor with 32-bit wide data bus can use up to four 8-bit wide memory banks, each can contain 1G locations. • If 32-bit number is transferred, all four banks are selected. • For 16-bit number, two banks. • For 8-bit number, one bank.

  21. Memory Interfacing

  22. I/O Devices • I/O devices allow the microprocessor to communicate with the outside world. • This is what makes the microprocessor “useful”. • Similar to memory interfacing, I/O interfacing also uses the data and address lines. • Data lines are still used to send/receive data from the I/O device. • However, the address lines are used to specify the port number, which specifies the I/O device to be accessed.

  23. I/O Instructions • There are two basic I/O instructions: • IN – to read data from I/O device • OUT – to write data to I/O device • Format: • IN dest, src • OUT dest, src • There are also instructions INS and OUTS: • Used to transfer strings of data between memory and I/O device. • Found in all Intel microprocessors except 8086 and 8088.

  24. I/O Instructions • There are two ways to specify the I/O address in IN/OUT instructions: • Fixed address • 8-bit address. • Address specified as an immediate value. • Variable address • 16-bit address. • Address is stored in DX. • The data register used for IN/OUT must always be AL, AX or EAX (depending on data length).

  25. I/O Instructions • The first 256 I/O port addresses (00H–FFH) are accessed by both fixed and variable I/O instructions. • I/O address from 0100H to FFFFH is only accessed by the variable I/O address. • I/O ports are always 8-bit in width (i.e. the data size is 8-bit). • A 16-bit port is actually two consecutive 8-bit ports being addressed. • A 32-bit port is actually four consecutive 8-bit ports being addressed.

  26. Types of I/O Interfacing • There are two different methods of I/O interfacing: • Isolated I/O • Memory-mapped I/O • Isolated I/O uses the IN, OUT, INS and OUTS instructions to transfer data to/from I/O device. • Memory mapped I/O transfer data to I/O device simply by using any instruction that references the memory.

  27. Isolated I/O • The word ‘isolated’ refers to the concept where the I/O address space is separated from memory address space. • Access to the I/O address space must be done using IN, OUT, INS and OUTS instructions. • Control signals such as M/IO are required to indicate whether the microprocessor is accessing the memory or I/O.

  28. Memory-mapped I/O • There is only one single address space for both memory and I/O. • Memory-mapped I/O does not use the IN, OUT, INS and OUTS instructions. • It uses any instruction that transfers data between the microprocessor and memory, such as MOV. • Advantage: simple to implement in a program. • Disadvantage: it takes up a portion of the system memory and therefore reduces the amount of memory available to applications. • This is the reason why if you install 4GB of RAM on a PC running 32-bit Windows, you cannot get the full 4GB.

  29. Personal Computer I/O Map • This diagram shows an example of I/O map for a PC. • The I/O map shows the I/O address for different peripherals. • I/O space between ports 0000H and 03FFH is normally reserved for the system and ISA bus. • Ports at 0400H–FFFFH are generally available for user applications, main-board functions, and the PCI bus. • On Windows, you can see this by going to Control Panel  System  Device Manager (on Hardware tab).

  30. Synchronizing with I/O Device • Many I/O devices accept or release data slower than the microprocessor. • The microprocessor can only read/write an I/O device when the device is ready to do so. • But how can we know whether the device is ready? • There are two methods to synchronize with I/O devices: • Using interrupt • Polling

  31. Synchronizing with I/O Device • If interrupt is used, the device will send an interrupt signal to the microprocessor when it is ready. • Recall hardware interrupt discussed in Chapter 5. • The interrupt service routine will then be executed to perform the necessary operation. • If polling is used, the program which performs the I/O operation will enter a loop to keep checking whether the device is ready. • There is normally a pin connection on the device that can be read for this purpose. • The disadvantage of this is that while doing polling, the program will only do this and cannot do other tasks.

  32. Direct Memory Access (DMA) • DMA is another method of transferring data to/from I/O devices. • However, it differs from isolated and memory-mapped I/O in the sense that the transfer is done without the use of the microprocessor. • Data transfer is done directly between memory and I/O devices. • DMA read transfers data from memory to I/O device. • DMA write transfers data from I/O device to memory. • This frees the microprocessor from the I/O operation and allows it to do other work.

  33. Direct Memory Access (DMA) • With DMA, the microprocessor would only need to initiate the DMA operation. • The HOLD and HLDA pins are used for this purpose. • While the data transfer is in progress, the microprocessor can continue doing other work. • This is essential in keeping the microprocessor productive. • Without the use of DMA, the microprocessor will be busy doing the data transfer, which is a very slow operation (compared to the microprocessor’s speed). • The only operation that the microprocessor cannot do within this time is another I/O operation. • Address and data bus is blocked for DMA data transfer.

  34. Direct Memory Access (DMA) • When the data transfer is done, the DMA controller will send an interrupt to the microprocessor. • DMA is commonly used with I/O devices that require bulk data transfer. • Disk drive controllers • Graphics cards • Sound cards • Network cards • DMA is also used for intra-chip data transfer in multi-core processors.

  35. Bus Interface • Allow external devices to be connected to the computer’s motherboard. • Consequently, allow the devices to be accessed from software running on the computer. • There have been many bus interface technologies. Among them are: • ISA (industry standard architecture) bus • PCI (peripheral component interconnect) bus • PCIe (PCI Express) bus • AGP (advanced graphics port) • USB (universal serial bus)

  36. ISA Bus • ISA bus has been around since the beginning of IBM PC. • Popularly used up until Pentium III computers. • There have been several versions: • 8-bit ISA bus • 16-bit ISA bus • 32-bit ISA bus, also called EISA (Extended ISA)

  37. PCI Bus • Starting from Pentium IV systems, PCI bus has started to replace ISA. • Main advantages of PCI bus over ISA: • Plug-and-play feature. • Allows the computer to automatically configure the PCI card. • Done using a series of registers at the PCI interface which contain information about the board. • Ability to function with a 64-bit data bus. • Supports both 32-bit and 64-bit data bus, with 32-bit address bus.

  38. PCI Bus • PCI interconnection is in parallel. • Speed of PCI bus: • 133 MBps (32-bit at 33 MHz) • 266 MBps (32-bit at 66 MHz or 64-bit at 33 MHz) • 533 MBps (64-bit at 66 MHz)

  39. AGP • As graphic adapter (video card) gets more advanced, the PCI bus is no longer adequate to transfer its data. • The industry ops for AGP instead. • AGP can provide a maximum data transfer rate of 2 GBps. • However, with the arrival of PCIe, AGP is no longer used.

  40. PCI Express Bus • Offers much higher speed compared to the PCI bus. • This is achieved through: • The use of high-speed serial interconnection. • Operating at a much higher speed of 2.5 GHz. • Each serial connection on the PCIe bus is called a lane. • A single lane is called referred to as (x1). • The PCIe standard defines slots and connectors for multiple widths: x1, x4, x8, x16, x32.

  41. PCI Express Bus • Data link speed per lane: • PCIe 1.x: 250 MBps • PCIe 2.x: 500 MBps • PCIe 3.0: 1 GBps • The total data link speed would depend on the number of lanes available on the PCIe card. For example: • x16 PCIe 3.0: 16 GBps • The high speed makes the PCIe bus suitable for cards which require a high speed data transfer such as a video card.

  42. USB • USB was designed to standardize the connection of computer peripherals. • External storage device, keyboard and mouse, sound card, video cam, printer, etc. • USB can even supply electric power to devices. • However USB is also used in other electronic devices such as smartphone, media player and gaming console. • This makes USB the most used interconnection bus today.

  43. USB • USB maximum speed: • USB 1.0/1.1: 1.5 MBps (12 Mbps) • USB 2.0: 60 MBps (480 Mbps) • USB 3.0: 640 MBps (5 Gbps) • The later versions are backward compatible with earlier versions. • To achieve the maximum speed, both the device and the USB interface must support the same version.

  44. Legacy I/O Ports • Before the existence of USB, external devices are connected to computers using the following ports: • Serial COM ports • Parallel printer interface (LPT) • Also known as parallel port. • Used mainly for printers. • PS/2 ports • Used for keyboard and mouse • Many new computer systems no longer have one or more of these ports installed.

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