ISA Bus Pinouts

ISA - Industry Standard Architecture. Most computers had ISA slots, but nowadays it is mostly replaced by PCI. The ISA bus protocol is quite simple. ISA supports 8 bit mode as well as 16 bit mode. If you have a look at a 16-bit ethernet card you'll see that it's connectors are split into two groups. The smaller one is only used in 16-bit mode - normally, the NIC looks on power up if the second group is connected and chooses thereupon the operation mode. Every ISA card is configured for a base address and an IRQ line. These two parameters make it possible to have more than one card on the ISA bus.

Here are the pinouts for the ISA Bus. The "Rear of Computer" means the back of the computer. Ex: If you had a 8 bit modem, it would be the side you would plug the phone cord into with the card in the slot.

ISA Bus (8-bit) Pinouts
          Rear of Computer/Looking from the top
                    :------:------:
             GROUND |- B1     A1 -| I/O CH CHK
          RESET DRV |- B2     A2 -| DATA 7
              +5VDC |- B3     A3 -| DATA 6
              IRQ 9 |- B4     A4 -| DATA 5
              -5VDC |- B5     A5 -| DATA 4
              DRQ 2 |- B6     A6 -| DATA 3
             -12VDC |- B7     A7 -| DATA 2
            -0 WAIT |- B8     A8 -| DATA 1
             +12VDC |- B9     A9 -| DATA 0
             GROUND |- B10   A10 -| -I/O RDY
             -SMEMW |- B11   A11 -| AEN
             -SMEMR |- B12   A12 -| ADDR 19
               -IOW |- B13   A13 -| ADDR 18
               -IOR |- B14   A14 -| ADDR 17
            -DACK 3 |- B15   A15 -| ADDR 16
              DRQ 3 |- B16   A16 -| ADDR 15
            -DACK 1 |- B17   A17 -| ADDR 14
              DRQ 1 |- B18   A18 -| ADDR 13
           -REFRESH |- B19   A19 -| ADDR 12
      CLK (4.77MHz) |- B20   A20 -| ADDR 11
              IRQ 7 |- B21   A21 -| ADDR 10
              IRQ 6 |- B22   A22 -| ADDR 9
              IRQ 5 |- B23   A23 -| ADDR 8
              IRQ 4 |- B24   A24 -| ADDR 7
              IRQ 3 |- B25   A25 -| ADDR 6
            -DACK 2 |- B26   A26 -| ADDR 5
                T/C |- B27   A27 -| ADDR 4
               BALE |- B28   A28 -| ADDR 3
              +5VDC |- B29   A29 -| ADDR 2
       OSC(14.3MHz) |- B30   A30 -| ADDR 1
             GROUND |- B31   A31 -| ADDR 0
                    :------:------:
ISA Bus (16-bit) Pinouts
         Rear of Computer/Looking from the top
                    :------:------:
             GROUND |- B1     A1 -| I/O CH CHK
          RESET DRV |- B2     A2 -| DATA 7
              +5VDC |- B3     A3 -| DATA 6
              IRQ 9 |- B4     A4 -| DATA 5
              -5VDC |- B5     A5 -| DATA 4
              DRQ 2 |- B6     A6 -| DATA 3
             -12VDC |- B7     A7 -| DATA 2
            -0 WAIT |- B8     A8 -| DATA 1
             +12VDC |- B9     A9 -| DATA 0
             GROUND |- B10   A10 -| -I/O RDY
             -SMEMW |- B11   A11 -| AEN
             -SMEMR |- B12   A12 -| ADDR 19
               -IOW |- B13   A13 -| ADDR 18
               -IOR |- B14   A14 -| ADDR 17
            -DACK 3 |- B15   A15 -| ADDR 16
              DRQ 3 |- B16   A16 -| ADDR 15
            -DACK 1 |- B17   A17 -| ADDR 14
              DRQ 1 |- B18   A18 -| ADDR 13
           -REFRESH |- B19   A19 -| ADDR 12
      CLK (8.33MHz) |- B20   A20 -| ADDR 11
              IRQ 7 |- B21   A21 -| ADDR 10
              IRQ 6 |- B22   A22 -| ADDR 9
              IRQ 5 |- B23   A23 -| ADDR 8
              IRQ 4 |- B24   A24 -| ADDR 7
              IRQ 3 |- B25   A25 -| ADDR 6
            -DACK 2 |- B26   A26 -| ADDR 5
                T/C |- B27   A27 -| ADDR 4
               BALE |- B28   A28 -| ADDR 3
              +5VDC |- B29   A29 -| ADDR 2
       OSC(14.3MHz) |- B30   A30 -| ADDR 1
             GROUND |- B31   A31 -| ADDR 0
                    :------:------:
                    :------:------:
          -MEM CS16 |- D1     C1 -| -SBHE
          -I/O CS16 |- D2     C2 -| LADDR 23
             IRQ 10 |- D3     C3 -| LADDR 22
             IRQ 11 |- D4     C4 -| LADDR 21
             IRQ 12 |- D5     C5 -| LADDR 20
             IRQ 13 |- D6     C6 -| LADDR 19
             IRQ 14 |- D7     C7 -| LADDR 18
            -DACK 0 |- D8     C8 -| LADDR 17
              DRQ 0 |- D9     C9 -| -MEMR
            -DACK 5 |- D10   C10 -| -MEMW
              DRQ 5 |- D11   C11 -| DATA 8
            -DACK 6 |- D12   C12 -| DATA 9
              DRQ 6 |- D13   C13 -| DATA 10
            -DACK 7 |- D14   C14 -| DATA 11
              DRQ 7 |- D15   C15 -| DATA 12
              +5VDC |- D16   C16 -| DATA 13
            -MASTER |- D17   C17 -| DATA 14
             GROUND |- D18   C18 -| DATA 15
                    :------:------:



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