The EISA (Extended Industry Standard Architecture) or Enhanced ISA bus operated at 8MHz using a 8/16/32 bit data bus. The EISA interface was another PC Expansion Bus which was also compatible with ISA. An ISA card will work in a EISA slot, but an EISA board 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 that were 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 below for EISA signal names and pin out information.
The Board size and Pinout for the Extended Industry Standard Architecture [EISA] bus is shown below. The EISA bus may also be called the Enhanced ISA bus. The EISA bus is obsolete and should not be used for new systems. However the pin out table may be used for legacy computer systems.
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| 1 | Channel Check | Ground | CMD | GND | System Enable | Memory 16 bit select | LA7 | LA8 |
| 2 | Data 7 | Reset | START | +5 volt | Unlatched Address 22 | I/O 16bit Chip Select | GND | LA6 |
| 3 | Data 6 | +5v | EXRDY | +5 volt | Unlatched Address 23 | IRQ10 | LA4 | LA5 |
| 4 | Data 5 | IRQ9 | EX32 | Reserved | Unlatched Address 21 | IRQ11 | LA3 | +5 volt |
| 5 | Data 4 | -5v | GND | Reserved | Unlatched Address 20 | IRQ12 | GND | LA2 |
| 6 | Data 3 | DMA Request 2 | KEY | KEY | Unlatched Address 19 | IRQ15 | KEY | KEY |
| 7 | Data 2 | -12v | EX16 | Reserved | Unlatched Address 18 | IRQ14 | SD17 | SD16 |
| 8 | Data 1 | Zero Wait State | SLBURST | Reserved | Unlatched Address 17 | DMA ACK0 | SD19 | SD18 |
| 9 | Data 0 | +12v | MSBURST | +12 volt | Memory Read | DMA Request 0 | SD20 | GND |
| 10 | I/O Channel Ready | Ground | W/R | M/IO | Memory Write | DMA ACK5 | SD22 | SD21 |
| 11 | Address Enable | Real Memory Write | GND | LOCK | Data 8 | DMA Request 5 | GND | SD23 |
| 12 | Address 19 | Real Memory Read | RESERVED | RESERVED | Data 9 | DMA ACK6 | SD25 | SD24 |
| 13 | Address 18 | I/O Write | RESERVED | GND | Data 10 | DMA Request 6 | SD26 | GND |
| 14 | Address 17 | I/O Read | RESERVED | RESERVED | Data 11 | DMA ACK7 | SD28 | SD27 |
| 15 | Address 16 | DMA ACK3 | GND | BE3 | Data 12 | DMA request 7 | KEY | KEY |
| 16 | Address 15 | DMA Request 3 | KEY | KEY | Data 13 | +5v | GND | SD29 |
| 17 | Address 14 | DMA ACK1 | BE1 | BE2 | Data 14 | Master | SD30 | +5 volts |
| 18 | Address 13 | DMA Request 1 | LA31 | BEQ | Data 15 | Ground | SD31 | +5 volts |
| 19 | Address 12 | Refresh | GND | GND | - | - | MREQ | MAK |
| 20 | Address 11 | CLK | LA30 | +5 volts | - | - | - | - |
| 21 | Address 10 | IRQ7 | LA28 | BEQ | - | - | - | - |
| 22 | Address 9 | IRQ6 | LA27 | GND | - | - | - | - |
| 23 | Address 8 | IRQ5 | LA25 | LA26 | - | - | - | - |
| 24 | Address 7 | IRQ4 | GND | LA24 | - | - | - | - |
| 25 | Address 6 | IRQ3 | KEY | KEY | - | - | - | - |
| 26 | Address 5 | DMA ACK2 | LA15 | LA16 | - | - | - | - |
| 27 | Address 4 | Terminal Count | LA13 | LA14 | - | - | - | - |
| 28 | Address 3 | Address Latch En | LA12 | +5 volt | - | - | - | - |
| 29 | Address 2 | +5v | LA11 | +5 volt | - | - | - | - |
| 30 | Address 1 | Oscillator | GND | GND | - | - | - | - |
| 31 | Address 0 | Ground | LA9 | LA10 | - | - | - | - |
| The PCXT bus pinout uses the J1 A/B rows, and a PCAT bus pinout uses the J1 [A/B rows] and J2 [C/D rows] connectors. The PC EISA pinout uses all rows of both J1 and J2. The EISA bus added rows 'E', 'F', 'G', and 'H' under the XT and AT pins. The fingers are copper strips on the PWB spaced on 0.1 inch centers. The PCAT bus [ISA] was an up-grade to the original PCXT bus, and the EISA bus was an up-grade to the PC-AT bus. An ISA card will work in a EISA slot, but an EISA card will not work in an AT slot. The Pin Out for both bus types are shown in the table above. The connector positions and relationship to the board are shown in the two figures at the top of the page. Both figures show a PCAT card, but the first figure also shows an attached PCI bus. Example dimensions for the card sizes are provided. Some of the signal names provided in the pin-out table are not correct terms. For example the Address lines called out above would be called SA#, and the Data lines would be called SD#. The IBM compatible 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 fingers (19 per side), while the XT connector had 62 fingers (32 per side). The Personal Computer 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 Mother boards. |
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Engineering Design Key words: PC, Personal Computer, EISA, PCAT, PCXT, ISA, PCI, Industry Standard Architecture Bus, Extended Industry Standard Architecture, Pinout, P2/J2 Pinouts, P1/J1 Pin out, J1 (A/B), J2 (C/D), Pin Outs, Connector, Signal Names, Pin descriptions, Card size, PWB Board Mechanical Dimensions, Mechanics Description, Electrical Interface, Parallel Bus, Physical Interface, Obsolete interface, Obsoleted, No longer in use, Out-dated, Out-of-Date.
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