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Step 4: Configuring the AT488 Interface DMA Channel
1. The factory default DMA channel is 5. If this creates a conflict, reset jumpers DACK and DRQ
according to the figure. Both the DRQ and DACK jumpers must be set to the desired DMA channel
for proper operation.
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 AT class machine has seven DMA
channels. Channels 0 to 3 (8-bit), 5, 6, and 7 (16-bit) are available only in a 16-bit slot on a PC/AT-
class machine. Channel 2 is usually used by the floppy disk controller, and is 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. Channels 5 to 7 are 16-bit DMA channels and offer the highest throughput (up to 1
Megabyte per second). Channels 0 to 3 are 8-bit DMA channels and although slower, they offer
compatibility with existing GP488B applications that only made use of 8-bit DMA channels. 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/AT (with AT488)
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