Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 26)

2. Personal488 (with GP488B) I. HARDWARE GUIDES
I-10 Personal488 User’s Manual, Rev. 3.0
Interrupt Selection
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 0-7). 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.
Interrupt selection is illustrated in the following figure.
DMA Channel Selection
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 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 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. Configure the board according to which DMA channel, if any, is available.