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Chapter 3 Hardware
32 Reference Manual LittleBoard 550
Pin # Signal Descriptions (J1 Row B)
47 (B15) DACK3* DMA Acknowledge 3 – 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.
48 (B16) DRQ3
DMA Request 3 – Used by I/O resources to request DMA service. Must
be held high until associated DACK3 line is active.
49 (B17) DACK1* DMA Acknowledge 1 – 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.
50 (B18) DRQ1 DMA Request 1 – Used by I/O resources to request DMA service. Must
be held high until associated DACK1 line is active.
51 (B19) REFRESH*
Memory Refresh – This signal is driven low to indicate a memory refresh
cycle is in progress. Memory is refreshed every 15.6 usec.
52 (B20) SYSCLK System Clock – This is a free running clock typically in the 8MHz to
10MHz range, although its exact frequency is not guaranteed.
53 (B21) IRQ7 Interrupt Request 7 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
54 (B22) IRQ6
Interrupt Request 6 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
55 (B23) IRQ5 Interrupt Request 5 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
56 (B24) IRQ4 Interrupt Request 4 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
57 (B25) IRQ3
Interrupt Request 3 – Asserted by a device when it has pending interrupt
request. Only one device may use the request line at a time.
58 (B26) DACK2* DMA Acknowledge 2 – 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.
59 (B27) TC Terminal Count – This signal is a pulse to indicate a terminal count has
been reached on a DMA channel operation.
60 (B28) BALE
Buffered Address Latch Enable – This signal is used to latch the LA23 to
LA17 signals or decodes of these signals. Addresses are latched on the
falling edge of BALE. It is forced high during DMA cycles. When used
with AENx, it indicates a valid processor or DMA address.
61 (B29) +5V +5 volt power ±10%
62 (B30) OSC Oscillator – This clock signal operates at 14.3MHz. This signal is not
synchronous with the system clock (SYSCLK).
63 (B31) GND Ground
64 (B32) GND Ground
Notes: The shaded area denotes power or ground. The signals marked with * = Negative true logic.