ISA BUS Industry Standard Architecture Cahit Tark Gen

ISA BUS (Industry Standard Architecture) Cahit Tarık Genç

What is BUS ? n A bus connects all the internal computer components to the CPU and Main memory. n Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old ISA bus is being replaced by faster buses such as PCI.

I/O BUS n System Bus: Connecting to CPU, memory and Cache. q Address Bus q Data Bus q Control Bus n I/O Bus: Connecting to the above three buses is the "good old" standard I/O bus, used for slower peripherals (mice, modems, regular sound cards, low-speed networking) and also for compatibility with older devices. On almost all modern PCs this is the Industry Standard Architecture (ISA) bus.

Types of I/O Buses n n n PCI Local bus n AGP n PC-Card (PCMCIA) n USB n Fire Wire (IEEE-1394) ISA Micro Channel (MCA) n EISA n VESA Local bus (VL-bus)

I/O BUS n n ISA BUS EISA BUS PCI BUS AGP (8 -16 -bit) (32 or 64 -bit) (32 -bit)

ISA BUS In 1982 when ISA BUS appeared on the first PC the 8 -bit ISA bus ran at a modest 4. 77 MHZ – the same speed as Intel 8088. ISA BUS is extremely slow by today's standards and not suited to the use of a graphical operating system like Windows.

ISA BUS n In 1984 the IBM AT was introduced using the Intel 80286; at this time the bus was doubled to 16 bits (the 80286's data bus width) and increased to 8 MHz (the maximum speed of the original AT, which came in 6 MHz and 8 MHz versions and 24 address lines).

ISA BUS 8 -bit 16 -bit

ISA BUS 8 -bit ISA BUS 16 -bit ISA BUS Bus width 8 - bit Bus width 16 - bit Compatible with 8 bit ISA Compatible with 16 bit ISA Pins 62 Pins 98 Power +5 V, -5 V, +12 V, -12 V Clock 4. 7727266 MHz Clock 8. 333333 MHz

ISA BUS n is used with sound cards, disk drives or most network and video cards. 8 -bit ISA(XT) CARD 16 -bit ISA CARD

ISA BUS ISA Card

ISA BUS VESA connectors Additional connections converts to 16 bit ISA Original 8 bit ISA connectors

ISA BUS In the figure you can see the pinouts of the ISA BUS. The BUS is divided into two sides. The first side pins are named A 1 to A 31 and it is the components side. It consists of the address and data buses. The second side pins are named B 1 to B 31 and it is the solder side. This side contents the power pins and the signals related to interrupts and DMA transfers.

ISA BUS More DMA lines IRQ lines 8 - 15 Extra 8 bits of Extra 4 bits of I/O bus Address bus 16 bit IRQ lines clock 2 -7 More DMA lines 20 bits of Address bus ± 5, ± 12 V Power & G 8 bits of I/O bus Original 8 bit ISA

ISA BUS n n n n A 0 -A 19 (pins A 31 to A 12): This twenty lines are the address BUS. They can address 1 MB (2^20 bytes). D 0 -D 7 (pins A 9 to A 2): The data BUS consist of this eight data lines. AEN (pin B 11): It is used for the DMA controller to take over the data and address buses in a DMA transfer. GND (pins B 1, B 10, B 31): Connected to the ground of the computer. +5 V (pins B 3, B 29): 5 V DC output of the power source. -5 V (pin B 5): -5 V DC output. -12 V (pin B 7): -12 V DC output. +12 V (pin B 9): +12 V DC output. MEMW (pin B 11): The µP asserts this signal when doing a write to the memory. MEMR (pin B 12): The µP asserts this signal when doing a read from the memory. IOW (pin B 13): The µP asserts this signal when doing a write to a port. IOR (pin B 14): The µP asserts this signal when doing a read from a port. DACK 0 -DACK 3 (pins B 15, B 17, B 19 and B 26): The DMA controller sets this signals to let a device know that the DMA has the control of the buses. DRQ 1 -DRQ 3 (pins B 6, B 16 and B 18): Allow the peripheral boards to request the use of the buses. +T/C (pin B 27): The DMA controller sets this signal to let the peripheral know that the programmed number of bytes has been sent. IRQ 2 -IRQ 7 (pins B 4, B 21, B 22, B 23, B 24 and B 25): Interrupt signals. The peripheral devices sets this signals to request for the attention of the µP. ALE (pin 28): This signal is used for the µP to lock the 16 lower address BUS in a latch during a memory (or port) input/output operation. CLOCK (pin 20): Is the system clock. OSC (pin 30): Is a high frequency clock which can be used for the I/O boards.

Describing the Read operation of the ISA n CPU sends out a high on the ALE signal, then sends out the A 0 -A 19 lines. On the address of the target port to be read will be latched. Then the BUS takes the -IOR signal to a low level. So that the addressed device will take a data byte to the D 0 -D 7 data bus. The microprocessor will read then the data bus and take the IOR signal to a high again.

Describing the Read/Write operation of the ISA n The only difference between a memory read/write cycle and a port read/write cycle is that in a memory cycle the -MEMR and -MEMW signals will be asserted, working the same way as -IOR and -IOW do.

ISA BUS Memory A 0 to A 31 Address bus(32 bit) n n n Intel 80386 DX CPU D 0 to D 31 Data bus (32 bit) RD WR IO/M Control bus I/O bus (16 bit data) Keyboard Storage Printer Video Modem

Bus Structure of Intel 486 “ISA BRIDGE”

Bus Structure of Intel Pentium “North Bridge” “South Bridge”

Bus Structure of Intel Pentium NORTH BRIDGE CPU Bus PCI Bus FRAME# TRDY# IRDY# M/IO #(memory or i/o address) D/C# (Data or code) W/R# (Write or Read) Expansion Bus Controller AEN# BRDY# (Burst Ready) STOP# REQ# GNT# AD[31: 0] A 31 -A 3 (Address Lines) C/BE#[3: 0] BE 7# - BE 0# (Byte Enable Lines) D 31 -D 0 CLK

Bus Structure of Intel Pentium SOUTH BRIDGE PCI Bus ISA Bus MEMR# FRAME# MEMW# TRDY# ALE IRDY# Expansion Bus Controller STOP# REQ# GNT# IOR# IOW# INTA# AD[31: 0] A 23 -A 0 C/BE#[3: 0] D 23 -D 0 CLK

ISA BUS INTERRUPT SYSTEM n n n 16 -bit ISA bus chains two 8259 As together. IRQ 9 is used to re-route anything trying to use IRQ 2. Incorporated in chip set.

INTERRUPT CONTROLLER (IRQ 2) 8259 A IRQ 0 (8) IRQ 1 (9) IRQ 2 (10) IRQ 3 (11) IRQ 4 (12) IRQ 5 (13) IRQ 6 (14) IRQ 7 (15) 8259 A IRQ 0 IRQ 1 IRQ 2 IRQ 3 IRQ 4 IRQ 5 IRQ 6 IRQ 7 80 x 86 INTR

Elimination of ISA Bus n n ISA Bus is slow, hard to use and bulky. ISA plug in cards to be replaced by either PCI plug-in cards or USB add-on peripherals Limited number of interrupts. No central registry.

Elimination of ISA Bus n The ISA bus is limited to 24 bits of address. 2^24 = 16 MBytes. It means that an ISA card that uses DMA cannot physically access memory beyond 16 MBytes of RAM. This is a limitation of the ISA bus.

Elimination of ISA Bus n Motherboard gets 32 -bit data from ISA BUS at two times. Meanwhile at this time ISA BUS declares “wait state” to the motherboard. Therefore ISA BUS may reduce System Performance.

Elimination of ISA Bus n If you use a ISA based controller card such as Ultra SCSI - 40 Mb / sec or SCSI-2 Fast - 10 Mb / sec , you can expect no more than an 8 Mb per second transfer rate from your controller card.

Elimination of ISA Bus n n PCI cards have “Plug and Play” technology and can configure themselves, so Operating Systems distinguish them. ISA cards are more cumbersome to install than other cards because I/O addresses, interrupts and clock speed must be set using jumpers and switches on the card itself.

Elimination of ISA Bus Type MB/sec VL-bus 100 MBps VL-bus 132 MBps 32 -Bit PCI 132 MBps PCI-X 66 512 MBps PCI-X 133 1 GBps AGP x 1 264 MB/s AGP x 2 528 MB/s AGP x 4 1056 MB/s AGP x 8 2112 MB/s PCI Express x 1 500 MB/s PCI Express x 2 1000 MB/s PCI Express x 4 2000 MB/s PCI Express x 8 4000 MB/s PCI Express x 12 6000 MB/s PCI Express x 16 8000 MB/s