PC/PC-AT Description and Pin Outs
Eredeti link:
http://www.interfacebus.com/Design_Connector_PCAT.html
ISA (AT)bus: The ISA bus operates at 8MHz with an 8 and 16 bits data
bus, a 24 bit address bus, using +/- 12 volts, +/- 5 volts, and 15
Interrupt lines. The standard drive level is 24mA for all non
Open-Collector signals on the bus. The AT card used the standard (edge)
connector provided by the XT bus and added an additional (edge)
connector behind that with the same pin-spacing @ 0.1 inch
center-to-center. The additional connector has only 38 (19 per side)
fingers, while the XT connector had 62 (32 per side) fingers. The
Motherboard could then accept either an 8 or 16 bit card in an 8 bit
slot (XT), or (if the connector was provided) a 16 bit card in an AT
slot. A maximum number of 8 Expansion slots were provided on IBM
compatible Motherboards. The additional connector provided 4 additional
address lines , and 8 additional data lines. Some Interrupt lines are
reserved and the AT spec allowed interrupt sharing. A number of
different oscillators may be used to control timers, bus transfers, etc.
Refer to this page for a comparison of Video bus through-put for
different expansion buses. This page provides the PC-XT / PC-AT pinout.
By 2001, many computers started shipping with PCI only slots. But a
combination of ISA AT expansion slots, and PCI slots was still common.
The PC ISA bus is Obsolete and should not be used for new designs. In
fact, all of the buses listed here are obsolete, and were all replaced
by the PCI bus. But, because so many ISA cards and Mother boards were
produced many companies still support these form factors. By the middle
of 2004 many companies were shipping Mother Boards with PCI expansion
slots [which replaced the ISA slots] and PCI-Express slots, in a
combination of 1x PCIe slots and 16x PCIe slots, which replaced the AGP
expansion slots. As of 2005 PCI-express slots reside on a majority of
motherboards, but AGP expansion slots are still common [especially on
AMD based boards]. PCI slots still exist on all motherboards, and the
ISA expansion slots are all but gone. Only industrial PC motherboards
still offer ISA based motherboards. In addition; the Embedded Industrial
PC/104 specification (IEEE P966) still requires the ISA bus, in a
different form factor.
This page provides additional external links to PC Reference and
Information Sites
Additional Personal Computer [PC] Bus Information:
ISA (XT)bus: Obsolete; 4.77MHz @ 8 bits, +/- 12 volts, +/- 5 volts. The
XT bus used a 62 pin (.1" center) edge connector; 31 pins per card side.
Used a single oscillator of 14.31818MHz which was divided by 3. 8 Data
lines, 0 to 7 (LSB=0). 20 Address lines, 0 to 19 (LSB=0). 1 Clock line
(4.77MHz). 1 Reset line, 8 Interrupt lines. Some 8 bit cards have skirts
which extend the board below the depth of the top of the connector to
allow additional circuitry. These cards, with skirts, are not compatible
with the 16 bit AT bus. The XT bus uses connector J1 (A/B), AT uses J1
(A/B), J2 (C/D). A maximum number of 8 Expansion slots were provided on
IBM compatible Motherboards.
MCA (Micro Channel Architecture) bus: Obsolete; 10MHz @ 16 or 32 bits,
uP independent, asynchronous, IBM proprietary on PS2 computers. With bus
enhancements the speed reaches 80MBps, using clock doubling. The MCI bus
only appeared on IBM PS2 series of computers which have been off the
market for many years now. MCA description and pinout information is
listed on the MCA page.
EISA (Extended Industry Standard Architecture) or (Enhanced ISA) bus:
8MHz @ 8/16/32 bits data bus, 32 bit address bus; PC Expansion Bus,
compatible with ISA. An ISA card will work in a EISA slot, but an EISA
card will not work in an AT slot. All of the PC-XT and PC-AT fingers
reside on an EISA board/connector. The actual EISA fingers (pin) reside
below the XT and AT fingers on an EISA board. The EISA bus (in one mode)
used both edges of the clock, with the rising edge used to output
address, and the falling edge to place the data on the bus. Three other
transfer modes were available. The EISA bus does not allow the board
skirts common with the older XT cards. The EISA cards are the same size
as the AT cards. The new address lines are termed "LA#", all address
lines are latched. Refer to the EISA Pinout table for signal names and
pin out information.
PCI (Peripheral Component Interconnect) bus: The Peripheral Component
Interface 'PCI' [Parallel] Bus was originally developed as a local bus
expansion for the PC. The first version of the PCI bus ran at 33MHz with
a 32 bit bus (133MBps), the current version runs at 66MHz with a 64 bit
bus. The PCI bus operates either synchronously or asynchronously with
the "mother Board bus rate: The PCI bus is microprocessor independent.
The page contains the PCI connector Pin-Outs. The PCI bus replaced the
PCAT bus on most Mother Boards.
PISA (PCI + ISA) bus: ~PC Expansion Bus. A normal ISA card with an
additional row of pins above, used for the PCI bus. A passive backplane
which moves all active devices off the Mother-Board and onto a single
card. The controller card used in the system has fingers [edge
connectors] for both PCI and the ISA bus, the Mother Board only
connectors. This allows additional cards to be added to the mother board
which use either the ISA or PCI buses. Because only connectors reside on
the motherboard, repair time is increased, and down time is decreased.
The standard is PICMG-xx. The specification is used in embedded or
industrial computer systems.
VESA (Video Electronic Standards Association)/Local bus (VLB or VL-Bus):
had a bus speed of 33MHz using either 16-bit or 32-bit data transfers,
30 address bits were provided. A 64 bit bus was also available by
multiplexing the additional upper 32 bits on to address bus. A maximum
of three devices may be connected to the bus. Best speed is seen in the
Burst mode: Single address followed by 4 data transfers. Supports bus
mastering.
The VLB resides on a standard 16 bit ISA card with the additional pins
required by the VLB interface residing after the ISA pins, allowing an
ISA card to use the same slot. A VLB card does not need to use the ISA
bus and may only require the VLB connector pins. Rev 2 of VLB
multiplexed 32 bit of data onto the address bus, producing a 64 bit data
bus. The version 2 card is back-ware compatible. The VLB connector is
keyed at pins 46 and 47. The pinout and a short description is provided
on the VESA Local Bus page.
Because this bus used the same bus structure as the 486, it could only
be used with the 486 class of processors, with the advent of the Pentium
processor and the PCI bus - this bus is now obsolete. This bus was
replaced with a deviant of the PCI bus called the AGP bus.
Apple Computer Buses
All other Computer Interface Buses
Card [Dimensions] Form Factors
PC AT and combined AT/PCI Bus Board Dimensions Full Size Detailed (with
Pin-Outs)
PC PCI Board Dimensions Half Size Board with Detailed Dimensions
PC-AT Board Size Drawing
PC Bus Interface IC Vendors
ISA bus use standard TTL logic levels for the AT and XT PC bus
interfaces. An input Low is 0 to 0.4v, High is 2.4v to Vcc. An output
Low is 0 to 0.8v, High is 2.0v to Vcc. The bus drive was reduced from
24mA used on the ISA bus to 4mA for the embedded PC/104 bus.
PC Chip Set Manufacturers
Memory Chip Manufacturers
Memory Module Manufacturers
Computer Processor Manufacturers
TTL Glue Logic Manufacturers
PC Bus Connector Manufacturers
Connector: Card Edge type, 100 pins, dual row (50 pins per side) on 0.1"
centers. The connector is keyed. For a comparison between the IBM XT
slot vs. the AT slot, refer to the connector below. The IBM XT slot used
the left portion of the connector (J1). The IBM AT slot added the right
most portion of the connector (J2). The AT slot used the entire
connector, J1 and J2. The connector has a card slot barrier which
divides the 98 Pin Connector into Groups of 62 and 36 Contacts.
PC Edge Connector Size
ISA Physical Connector
EDAC Inc.
FCI
Card Edge connector manufacturers are listed on the connector page.
Engineering Design Key words for this page: Personal Computer Bus, PC
Bus, Industry Standard Architecture Bus, ISA, AT Bus, Backplane bus,
Local Video Bus, Standard, Interface Standard, Specification, Spec,
Electrical Interface, IC, Parallel Bus, Physical Interface, Card
Dimensions and Form Factors, Engineering Description, Component
Manufacturers, OEM COTS, Connector, PinOut, Pin-Out, Expansion slots.