Measurement Computing Personal488 rev.3.0 - Manual (Page 49)

Personal488 for Windows 95/98/Me/NT/2000 04-09-01 Hardware Configuration Reference 4-9
The GP488B interface board may be set to interrupt the PC on the occurrence of certain hardware
conditions. The level of the interrupt generated is set by J4. The GP488B adheres to the “AT-style”
interrupt sharing conventions. When an interrupt occurs, the interrupting device must be reset by writing to
I/O address
02FX , where X is the interrupt level (from 0 to 7). This interrupt response level is set by
switches 1, 2, and 3 of SW1 which must be set to correspond to the J4 interrupt level setting.
Configuring the GP488B Interface DMA Channel
J3
C h an ne l 1
G P 4 8 8 B D M A C h a n n e l S ele c tio n s
C h an ne l 2 C h an ne l 3
The factory default DMA channel is 1. If this creates a conflict, reset jumper J3 according to the figure.
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.