Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 60)

II. SOFTWARE GUIDES - 8. Driver488/DRV 8B. Installation & Configuration
Personal488 User’s Manual, Rev. 3.0 II-45
Multiple Interface Management
When designing a complex data acquisition system, it might be necessary to have more than one
IEEE 488 bus interface controlled by the computer. Typical instances include: A system with more
than 15 devices, the use of distributed control or the simultaneous operation of multiple transactions.
System With More Than 15 Devices
The IEEE 488 electrical specification limits the number of devices on a single bus (including the
controller) to 15. While a bus expander, such as the Expander488, can increase that limit to 28,
complex systems may require two or more IEEE 488 buses and have more controllers.
In this case, two or more interfaces would be used, each configured as a System Controller. Because
they are attached to completely separate buses, the two interfaces do not affect each other. They can
have the same IEEE 488 bus address, and the addresses of the devices on one bus may be the same as
the addresses of the devices on the other bus.
Use of Distributed Control
Two or more IEEE 488 buses can also be useful when they have different functions. For example, a
computer might use one bus as a System Controller to control instruments, while using another bus as a
Peripheral, to communicate with another computer.
Simultaneous Operation of Multiple Transactions
Another use of two IEEE 488 buses is to allow simultaneous operation of two separate transactions.
Some instruments, such as spectrum analyzers, have the ability to send their results, through the
IEEE 488 bus, directly to a printer or a plotter. Such an instrument, along with a printer or plotter,
would be attached to one interface, while other devices would be attached to another IEEE 488
interface. The computer could configure the spectrum analyzer to plot its results and then pass control
to it, allowing it to control the printer or plotter. Meanwhile, the computer would be using the other
bus to control other equipment.
To allow such complex systems, Driver488/DRV supports as many as four interfaces on a single
computer. The
CONFIG program helps you to configure multiple interfaces and notifies you of possible
conflicts.
The examples in this manual assume, for the most part, that only one board is installed in the system,
and that it is accessed through the three device names given above for the first board. If multiple
interfaces are installed, then they are accessed in just the same manner as the first board, except that
different device names, as given above, are used. If, for example, two interfaces are installed, then a
BASIC program to use them might be:
100 OPEN “\DEV\IEEEIN” FOR INPUT AS #1
110 OPEN “\DEV\IEEEOUT” FOR OUTPUT AS #2
120 OPEN “\DEV\IEEEIN2" FOR INPUT AS #3
130 OPEN “\DEV\IEEEOUT2" FOR OUTPUT AS #4
140 PRINT#2,"OUTPUT 10;R0X"
150 PRINT#4,"OUTPUT 10;R1X"
where line 140 sends R0X to device 10 on the IEEE 488 bus controlled by board 1, and line 150 send
R1X to device 10 on the second IEEE 488 bus. Because they are on two physically different IEEE 488
buses, there is no confusion as to which device 10 is being accessed.
Note: If installation or configuration problems exist, refer to “Section IV: Troubleshooting.”