Hardware Reference
In-Depth Information
The following table describes each of the signals present on the 62-way ISA
expansion bus connector:
Pin number
Abbreviation
Direction
Signal
Function
A1
/IOCHK
I
I/O channel
Taken low to indicate a parity error in a memory
check
or I/O device
A2
D7
I/O
Data 7
Data bus line
A3
D6
I/O
Data 6
Data bus line
A4
D5
I/O
Data 5
Data bus line
A5
D4
I/O
Data 4
Data bus line
A6
D3
I/O
Data 3
Data bus line
A7
D2
I/O
Data 2
Data bus line
A8
D1
I/O
Data 1
Data bus line
A9
D0
I/O
Data 0
Data bus line
A10
/IOCHRDY
I
I/O channel
Pulsed low by a slow memory or I/O device
ready
to signal that it is not ready for data transfer
A11
AEN
O
Address
Issued by the DMA controller to indicate that a DMA
enable
cycle is in progress. Disables port I/O during a DMA
operation in which /IOR and /IOW may be asserted
A12
A19
I/O
Address 12
Address bus line
A13
A18
I/O
Address 13
Address bus line
A14
A17
I/O
Address 14
Address bus line
A15
A16
I/O
Address 15
Address bus line
A16
A15
I/O
Address 16
Address bus line
A17
A14
I/O
Address 17
Address bus line
A18
A13
I/O
Address 18
Address bus line
A19
A12
I/O
Address 19
Address bus line
A20
A11
I/O
Address 20
Address bus line
A21
A10
I/O
Address 21
Address bus line
A22
A9
I/O
Address 22
Address bus line
A23
A8
I/O
Address 23
Address bus line
A24
A7
I/O
Address 24
Address bus line
A25
A6
I/O
Address 25
Address bus line
A26
A5
I/O
Address 26
Address bus line
A27
A4
I/O
Address 27
Address bus line
A28
A3
I/O
Address 28
Address bus line
A29
A2
I/O
Address 29
Address bus line
A30
A1
I/O
Address 30
Address bus line
A31
A0
I/O
Address 31
Address bus line
B1
GND
n.a.
Ground
Ground/common 0 V
B2
RESET
O
Reset
When taken high this signal resets all expansion cards
B3
+
5 V
n.a.
+
5V DC
+
5 V supply voltage
B4
IRQ2
I
Interrupt request
Interrupt
level 2
request (highest priority)
B5
−
5 V
n.a.
−
5 V DC supply
−
5 V supply voltage
B6
DRQ2
I
Direct memory
Taken high when a DMA transfer is required.
access request
The signal remains high until the
level 2
corresponding /DACK line goes low
(
continued
)
