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Chapter 3 Hardware
34 Reference Manual LittleBoard 550
Pin # Signal Descriptions (J1 Row D)
27 (D6) IRQ15 Interrupt Request 15 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
28 (D7) IRQ14 Interrupt Request 14 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
29 (D8) DACK0*
DMA Acknowledge 0 – Used by DMA controller to select the I/O
resource requesting the bus, or to request ownership of the bus as a bus
master device. Can also be used by the ISA bus master to gain control of
the bus from the DMA controller.
30 (D9) DRQ0 DMA Request 0 – Used by I/O resources to request DMA service. Must
be held high until associated DACK0 line is active.
31 (D10) DACK5* DMA Acknowledge 5 – Used by DMA controller to select the I/O
resource requesting the bus, or to request ownership of the bus as a bus
master device. Can also be used by the ISA bus master to gain control of
the bus from the DMA controller.
32 (D11) DRQ5 DMA Request 5 – Used by I/O resources to request DMA service. Must
be held high until associated DACK5 line is active.
33 (D12) DACK6* DMA Acknowledge 6 – Used by DMA controller to select the I/O
resource requesting the bus, or to request ownership of the bus as a bus
master device. Can also be used by the ISA bus master to gain control of
the bus from the DMA controller.
34 (D13) DRQ6 DMA Request 6 – Used by I/O resources to request DMA service. Must
be held high until associated DACK6 line is active.
35 (D14) DACK7* DMA Acknowledge 7 – Used by DMA controller to select the I/O
resource requesting the bus, or to request ownership of the bus as a bus
master device. Can also be used by the ISA bus master to gain control of
the bus from the DMA controller.
36 (D15) DRQ7 DMA Request 7 – Used by I/O resources to request DMA service. Must
be held high until associated DACK7 line is active.
37 (D16) +5V +5 volt power ±10%
38 (D17) MASTER*
Bus Master Assert – This signal is used by an ISA board along with a
DRQ line to gain ownership of the ISA bus. Upon receiving a -DACK a
device can pull -MASTER low which will allow it to control the system
address, data, and control lines. After -MASTER is low, the device
should wait one CLK period before driving the address and data lines,
and two clock periods before issuing a read or write command.
39 (D18) GND Ground
40 (D19) GND Ground
Notes: The shaded area denotes power or ground. The signals marked with * = Negative true logic.