ISA Connections

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ISA Card-Edge Connector

The ISA card-edge connector is used to connect peripheral cards to the motherboard of PC compatible computers.  The "ISA Connector" is actually two card-edge connectors one 62-pin, one 36-pin.  The 36-pin connector (designated as having pins C1-D18) was added for 16-bit I/O at the time the IBM PC/AT was developed.

Here's a look at an ISA card, showing the connector.

ISA Card

 

Here's what the ISA motherboard connector looks like:

ISA Motherboard Connector

 

 

Pin Name Direction Description
A1 /I/O CH CK Card-to-PC I/O channel check; active low=parity error
A2 D7 Bidirectional Data bit 7
A3 D6 Bidirectional Data bit 6
A4 D5 Bidirectional Data bit 5
A5 D4 Bidirectional Data bit 4
A6 D3 Bidirectional Data bit 3
A7 D2 Bidirectional Data bit 2
A8 D1 Bidirectional Data bit 1
A9 D0 Bidirectional Data bit 0
A10 I/O CH RDY Card-to-PC I/O Channel ready, pulled low to lengthen memory cycles
A11 AEN PC-to-Card Address enable; active high when DMA controls bus
A12 A19 PC-to-Card Address bit 19
A13 A18 PC-to-Card Address bit 18
A14 A17 PC-to-Card Address bit 17
A15 A16 PC-to-Card Address bit 16
A16 A15 PC-to-Card Address bit 15
A17 A14 PC-to-Card Address bit 14
A18 A13 PC-to-Card Address bit 13
A19 A12 PC-to-Card Address bit 12
A20 A11 PC-to-Card Address bit 11
A21 A10 PC-to-Card Address bit 10
A22 A9 PC-to-Card Address bit 9
A23 A8 PC-to-Card Address bit 8
A24 A7 PC-to-Card Address bit 7
A25 A6 PC-to-Card Address bit 6
A26 A5 PC-to-Card Address bit 5
A27 A4 PC-to-Card Address bit 4
A28 A3 PC-to-Card Address bit 3
A29 A2 PC-to-Card Address bit 2
A30 A1 PC-to-Card Address bit 1
A31 A0 PC-to-Card Address bit 0
B1 GND  N/A Ground
B2 RESET PC-to-Card Active high to reset or initialize system logic
B3 +5V   +5 VDC
B4 IRQ2 Card-to-PC Interrupt Request 2
B5 -5VDC PC-to-Card -5 VDC
B6 DRQ2 Card-to-PC DMA Request 2
B7 -12VDC PC-to-Card -12 VDC
B8 /NOWS Card-to-PC No WaitState
B9 +12VDC PC-to-Card  +12 VDC
B10 GND N/A Ground
B11 /SMEMW PC-to-Card System Memory Write
B12 /SMEMR PC-to-Card System Memory Read
B13 /IOW PC-to-Card I/O Write
B14 /IOR PC-to-Card I/O Read
B15 /DACK3 PC-to-Card DMA Acknowledge 3
B16 DRQ3 Card-to-PC DMA Request 3
B17 /DACK1 PC-to-Card DMA Acknowledge 1
B18 DRQ1 Card-to-PC DMA Request 1
B19 /REFRESH Bidirectional Refresh
B20 CLOCK PC-to-Card System Clock (67 ns, 8-8.33 MHz, 50% duty cycle)
B21 IRQ7 Card-to-PC Interrupt Request 7
B22 IRQ6 Card-to-PC Interrupt Request 6
B23 IRQ5 Card-to-PC Interrupt Request 5
B24 IRQ4 Card-to-PC Interrupt Request 4
B25 IRQ3 Card-to-PC Interrupt Request 3
B26 /DACK2 PC-to-Card DMA Acknowledge 2
B27 T/C PC-to-Card Terminal count; pulses high when DMA term. count reached
B28 ALE PC-to-Card Address Latch Enable
B29 +5V PC-to-Card +5 VDC
B30 OSC PC-to-Card High-speed Clock (70 ns, 14.31818 MHz, 50% duty cycle)
B31 GND  N/A Ground
       
C1 SBHE Bidirectional System bus high enable (data available on SD8-15)
C2 LA23 Bidirectional Address bit 23
C3 LA22 Bidirectional Address bit 22
C4 LA21 Bidirectional Address bit 21
C5 LA20 Bidirectional Address bit 20
C6 LA18 Bidirectional Address bit 19
C7 LA17 Bidirectional Address bit 18
C8 LA16 Bidirectional Address bit 17
C9 /MEMR Bidirectional Memory Read (Active on all memory read cycles)
C10 /MEMW Bidirectional Memory Write (Active on all memory write cycles)
C11 SD08 Bidirectional Data bit 8
C12 SD09 Bidirectional Data bit 9
C13 SD10 Bidirectional Data bit 10
C14 SD11 Bidirectional Data bit 11
C15 SD12 Bidirectional Data bit 12
C16 SD13 Bidirectional Data bit 13
C17 SD14 Bidirectional Data bit 14
C18 SD15 Bidirectional Data bit 15
D1 /MEMCS16 Card-to-PC Memory 16-bit chip select (1 wait, 16-bit memory cycle)
D2 /IOCS16 Card-to-PC I/O 16-bit chip select (1 wait, 16-bit I/O cycle)
D3 IRQ10 Card-to-PC Interrupt Request 10
D4 IRQ11 Card-to-PC Interrupt Request 11
D5 IRQ12 Card-to-PC Interrupt Request 12
D6 IRQ15 Card-to-PC Interrupt Request 15
D7 IRQ14 Card-to-PC Interrupt Request 14
D8 /DACK0 PC-to-Card DMA Acknowledge 0
D9 DRQ0 Card-to-PC DMA Request 0
D10 /DACK5 PC-to-Card DMA Acknowledge 5
D11 DRQ5 Card-to-PC DMA Request 5
D12 /DACK6 PC-to-Card DMA Acknowledge 6
D13 DRQ6 Card-to-PC DMA Request 6
D14 /DACK7 PC-to-Card DMA Acknowledge 7
D15 DRQ7 Card-to-PC DMA Request 7
D16 +5 V PC-to-Card  
D17 /MASTER Card-to-PC Used with DRQ to gain control of system
D18 GND  N/A Ground

 

Note: B8 was /CARD SLCDTD on the XT ("card selected", activated by cards in XT's slot J8)
 

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