Subject Name: Microprocessors Subject Code:10EC46 Department: Electronics and Communication Date:30-5-2015

Engineered for Tomorrow UNIT:7 SYSTEM BUS STRUCTURE

Contents Basic 8086 configurations. Minimum mode Maximum mode Bus Interface Peripheral component interconnect(PCI) Parallel printer interface(LPT) Universal serial bus(USB)

BASIC 8086 CONFIGURATION In order to adapt to as many situations as possible in the 8086 have been given two modes of operation, the minimum mode. the maximum mode.

Minimum Mode Operation similar to 8085 (8 bit processor) MN/MX* pin connected to +5 V 8-bit peripherals can be used with 8088/8086 Fig: Block Diagram of Minimum mode operation

Maximum Mode Enhanced Operation used whenever a coprocessor is used with 8088/8086 MN/MX* pin connected to GND 8288 Bus Controller required to generate extra signals

Bus interface

PCI Bus Work began in 1990 Intel began work on a new bus for their Pentium systems Processor independent To support higher bandwidth requirements of window-based systems Original version (1.0) developed by Intel in 1990 Version 2 in 1993 Version 2.1 in 1995 Version 2.2 introduced power management for mobile systems

PCI bus(cont..) Transaction Control Signals Cycle Frame (FRAME#) Indicates start of a bus transaction Also indicates the length of the bus transaction cycle Initiator Ready (IRDY#) During Write transaction: Indicates the initiator has placed data on AD lines During Read transaction: Indicates the initiator is ready to accept data Target Ready (TRDY#) Complements IRDY# signal IRDY# and TRDY# together implement handshake to transfer data

PCI bus(cont..) Transaction Control Signals Stop Transaction (STOP#) Target asserts this to tell initiator that it wants to terminate the current transaction Initialization Device Select (IDSEL) Used as a chip select for configuration read and write transactions Device Select (DEVSEL#) Selected target asserts this to tell the initiator that it is present Bus Lock (LOCK#) Imitator uses this to lock the target to execute atomic transactions

PCI bus(cont..) Bus Arbitration Signals Uses centralized bus arbitration with independent request and grant lines Bus Request (REQ#) A device asserts when it needs the bus Bus Grant (GNT#) Bus arbiter asserts this signal to indicate allocation of the bus Bus arbitration can overlap execution of another transaction Improves PCI performance

PCI bus(cont..) Error Reporting Signals Parity Error (PERR#) All devices are expected to report this error Exceptions exist E.g. when transmitting video frames System Error (SERR#) Any PCI device can generate this signal To indicate address and other errors Typically connected to NMI (non-maskable interrupt)

PCI bus(cont..) 64-bit Extension Signals Address/Data Lines (AD[32 - 63]) Extension to 64 bits Command bus (C/BE#[4 - 7]) Extended by 4 lines to handle 8 bytes Request 64-Bit Transfer (REQ64#) Indicates to target that initiator likes 64-bit transfers Acknowledge 64-Bit Transfer (ACK64#) Target indicates that it is capable of 64-bit transfers Parity Bit for Upper Data (PAR64) Even parity for upper 32 AD bits and four command lines

PCI bus(cont..) Interrupt Request Lines Four interrupt lines INTA#, INTB#, INTC#, INTD# Not shared Additional signals To support snoopy cache protocol IEEE 1149.1 boundary scan signals Allows in-circuit testing of PCI devices M66En signal to indicate bus frequency Low: 33 MHz High: 66 MHz

PCI bus(cont..) A command value is placed on C/BE lines during the address phase I/O operations I/O Read and I/O Write Memory operations Standard memory operations Memory Read and Memory Write Bulk memory operations Memory Read Line Memory Read Multiple Memory Write-and-Invalidate

PCI Operations PCI read

PCI WRITE

PCI Bus Arbitration Uses centralized arbitration Independent grant and request lines REQ# and GNT# lines for each device Does not specify a particular policy Mandates the use of a fair policy Two delay components Arbitration overlaps with another transaction execution

PCI Bus Hierarchies Allows bus hierarchies Built using PCI-to-PCI bridges Need two bus arbiters One for the primary bus One for the secondary bus Example: Intel 21152 PCI-to-PCI bridge Secondary bus can connect up to 4 devices One internal arbiter available Can be used on the secondary side Need external arbiter for the primary side

PCI Bus Hierarchies(Cont…)

PCI Delays 66 MHz implementations pose serious design challenges All delays are cut in half compared to 33 MHz clock

THE PARALLEL PRINTER INTERFACE (LPT) The parallel printer interface (LPT) is located on the rear of the PC. LPT stands for line printer. The printer interface gives the user access to eight lines that can be programmed to receive or send parallel data. The parallel port (LPT1) is normally at I/O addresses 378H, 379H, & 37AH from DOS or by using a driver in Windows The secondary (LPT2) port, if present, is located at 278H, 279H, & 27AH. The connectors are shown in Figure 15–13

The connectors used for the parallel port. the Centronics interface on the parallel port uses two connectors a 25-pin D-type on the back of the PC a 36-pin Centronics on the back of the printer . The parallel port can work as both a receiver and a transmitter at its data pins (D0–D7). allows other devices such as CD-ROMs, to be connected to and used by the PC through port Anything that can receive and/or send data through an 8-bit interface can and often does connect to the parallel port (LPT1) of a PC.

Ports 378H, 379H, and 37AH as used by the parallel port. the data port (378H) the status register (379H) an additional status port (37AH) note that some of the status bits are true when logic 0

THE UNIVERSAL SERIAL BUS The universal serial bus (USB) has solved a problem with the PC system. Current PCI sound cards use internal PC power, which generates a lot of noise. USB allows the sound card to have its own power supply, for high-fidelity sound with no 60 Hz hum Other benefits are ease of connection and access to up to 127 different connections. The interface is ideal for keyboards, sound cards, simple video-retrieval, and modems. Data transfer speeds are 480 Mbps for full-speed USB 2.0 operation. 11 Mbps for USB 1.1 compliant transfers 1.5 Mbps for slow-speed operation Cable lengths are limited to five meters for the full-speed interface and three meters maximum for the low-speed interface. Maximum power through the cables is rated at 100 mA, maximum current at 5.0 V.

The Connector two types of connectors are specified, both are in use there are four pins on each connector, with signals indicated further. the +5.0 V and ground can power devices connected to the bus data signals are biphase signals when +data are at 5.0 V, –data are at zero volts and vice versa

USB Data Data signals are biphase signals generated using a circuit such as shown in Fig 15–16. The line receiver is also shown. A noise-suppression circuit available from Texas Instruments (SN75240) is placed on the transmission pair Once the transceiver is in place, interfacing to the USB is complete. Fig: The interface to the USB using a pair of CMOS buffers.

Fig NRZI encoding used with the USB. USB uses NRZI (non-return to zero, inverted) encoding to transmit packet data this method does not change signal level for the transmission of logic 1 signal level is inverted for each change to logic 0 Fig  NRZI encoding used with the USB.

USB data transmision(Cont..) Actual data transmitted includes sync bits, a method called bit stuffing, because it lengthens the data stream. If logic 1 is transmitted for more than 6 bits in a row, the bit stuffing technique adds an extra bit (logic 0) after six continuous 1s in a row. Bit stuffing ensures the receiver can maintain synchronization for long strings of 1s and data are always transmitted with the least-significant bit first, followed by subsequent bit

a bit-stuffed serial data stream and the algorithm used to create it from raw digital serial data

USB Commands To begin communication, sync byte 80H is transmitted first, followed by the packet identification byte (PID). The PID contains 8 bits. only the rightmost 4 bits contain the type of packet that follows, if any The leftmost 4 bits of the PID are the ones complementing the rightmost 4 bits.

The types of packets and contents found on the USB.

The USB Bus Node National Semiconductor produces a USB bus interface easy to interface to the processor. Connect this device using non-DMA access: connect the data bus to D0–D7 connect control inputs RD, WR, and CS and a 24 MHz fundamental crystal across XIn and XOut pins The USB bus connection is located on the D– and D+ pins. Figure 15–20 shows a USBN9604 USB node.

USBN9604 is a USB bus transceiver that can receive and transmit USB data this provides an interface point to the USB bus for a minimal cost of about two dollars

  The USBN9604 interfaced to a microprocessor at I/O addresses 300H and 301H.

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