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Chapter 3 Hardware Overview
PCI-4451/4452 User Manual 3-12
©
National Instruments Corporation
A PCI-4451/4452 device can use either its internal 20 MHz timebase or a
timebase received over the RTSI bus. In addition, if you configure the
device to use the internal timebase, you can program the device to drive its
internal timebase over the RTSI bus to another device that you program to
receive this timebase signal. The default configuration at startup is to use
the internal timebase without driving the RTSI bus timebase signal. This
timebase is software-selectable.
Selecting Sample/Update Clock Frequency
The two analog input channels of the PCI-4451 and the four inputs of the
PCI-4452 are simultaneously sampled at any software-programmable rate
from 5.0 kS/s to 204.8 kS/s in 190.7 µS/s increments (worst case). The
devices use direct digital synthesis (DDS) technology so that you can
choose the correct sample rate required for your application. All the input
channels acquire data at the same rate. One input channel cannot acquire
data at a different rate from another input channel.
The two analog output channels of the PCI-4451 are updated
simultaneously at any software programmable rate from 1.25 kS/s to
51.2 kS/s in 47.684 µS/s increments (worst case). The input sample rate
and output update rate on the PCI-4451 are synchronized and derived from
the same DDS clock. The input and output clocks may differ from each
other by a factor of 2 (1, 2, 4, 8, …, 128) while still maintaining their
synchronization as long as the lower bounds for update and sample rate are
maintained. All the output channels update data at the same rate. One
output channel cannot update data at a different rate from another output
channel.
The DDS clock signal and the synchronization start signal are transmitted
to other PCI-DSA devices via the RTSI bus. The PCI-4451/4452 can also
receive these signals to synchronize the acquisition or waveform generation
with other devices. In a multidevice system, a master device would drive
the clock and synchronization signal to other slave or receiving devices.
User.book Page 12 Tuesday, April 14, 1998 10:20 AM