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Step 4: Configuring the GP488B Interface DMA Channel
1. The factory default DMA channel is 1. If this creates a conflict, reset jumper J3 according to the
figure.
2. If reset, record the new DMA channel being used.
Direct Memory Access (DMA) is a high-speed method of transferring data from or to a peripheral, such
as a digitizing oscilloscope, to or from the PC's memory. The PC has four DMA channels, but Channel
0 (Disabled) is used for memory refresh and is not available for peripheral data transfer. Channel 2 is
usually used by the floppy disk controller, and is also unavailable. Channel 3 is often used by the hard
disk controller in PCs, XTs, and the PS/2 with the ISA bus, but is usually not used in ATs. So,
depending on your hardware, DMA Channels 1 and possibly Channel 3 are available. Under some rare
conditions, it is possible for high-speed transfers on DMA Channel 1 to demand so much of the
available bus bandwidth that simultaneous access of a floppy controller will be starved for data due to
the relative priorities of the two channels.
Personal488 User's Manual For Windows 95 and Windows NT
Personal488 (with GP488B)
27
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