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Installation and Configuration Section Two
GPIB-PC User Manual 2-8 ©National Instruments Corp.
• What DMA channel, if any, the board uses.
• Whether it uses high-speed or normal timing when transmitting
data to a device. With normal timing, there is a delay of at
least 2 µsec after the data is placed on the GPIB before the
Data Valid (DAV) line is asserted. With high-speed timing,
this delay is decreased to about 500 nsec.
• The Internal Clock Frequency for a PC-IIA. This is the value of
the internal PC bus clock.
Default Configurations
Just as the hardware has factory default settings for switches and
jumpers, the software also has factory default configurations. For
example, the default device names of the 16 GPIB devices are DEV1
through DEV16, but you might wish to assign more descriptive names to
each device, such as METER for a digital multimeter.
You can also use IBCONF to look at the current default settings in the
handler file.
If you do not make changes using IBCONF, the default characteristics of
the software remain in effect.
Primary Default Characteristics
The following are the primary default characteristics of the handler.
• There are 16 active devices with symbolic names DEV1 through
DEV16.
• GPIB addresses of these devices are the same as the device
number; for example, DEV1 is at address 1.
• The 16 devices are assigned to GPIB0 as their access board.
GPIB0 is the symbolic name of the first GPIB-PC board in your
system. If you have an additional GPIB-PC in your system, its
symbolic name is GPIB1.
• Each GPIB-PC is System Controller of its independent bus and
has a GPIB address of 0.
• The END message is sent with the last byte of each data
message to a device. Each data message that is read from a