Hardware Reference
In-Depth Information
Figure 8.7
Typical IEEE-488 bus configuration (star configuration)
a
star bus
arrangement in which one device is connected to three others. Any
combination of these two methods is possible provided that the restrictions
mentioned in the previous paragraph are obeyed.
In all cases it is advisable to ensure that no instrument cable exceeds 4 m
in length and that good quality double shielded (foil and braid plus earth) and
twisted pair conductors are used. Connectors can be single or piggyback types
in order to permit daisy chaining of devices. Standard cable lengths of 1, 2, and
4 m are available from various suppliers (see Appendix J).
IEEE-488 controllers
IEEE-488 controllers (or
GPIB controllers
) are available in a variety of forms
including ISA, PCI, PC/104, and PCMCIA types. ISA and PC/104 cards (which
are not 'plug-and-play' compatible) usually require base address selection by
means of DIP switches (see Figure 8.8) or by means of PCB links. Since most
computers have base address 300H (768 decimal free), this is usually the default
setting for this type of board. Other typical addresses include 310H and 330H.
A typical DIP/link address setting convention (as used on Metrabyte Computing
Corporation's cards) is as follows:
DIP/link no.
Hex. value
Decimal value
Default setting
9
200H
512
ON
8
100H
256
ON
7
80H
128
OFF
6
40H
64
OFF
5
20H
32
OFF
4
10H
16
OFF
The base address is found by simply adding the values of the switches/links
that are in the ON position. Thus the default address in the table shown above is
