Measurement Computing Personal488 rev.1.0 - Manual (Page 31)

Personal488 for Windows 95/98/Me/NT/2000/XP 889496 Hardware Configuration Reference 4-5
Configuring the AT488 Interface DMA Channel
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. 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 and
GP488B/MM 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.