PCIe-24DSI32
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General Standards Corporation Ph:(256)880-8787 FAX:(256)880-8788 Email: [email protected]
3-8
3.6 Input Sampling Control
The local controller establishes the following input sampling parameters:
a. Sample rate,
b. Phase, or skew,
c. Channel synchronization.
The effective input bandwidth is determined by the sample rate, while phase and
synchronization control the relative timing of sampling between multiple channels. Phase and
synchronization are considerations in applications that require consistent relative timing of
sampling among multiple channels or multiple boards.
Clocking multiple converters from a single sample rate clock prevents the
sampling drift
that
occurs when converters are clocked from different sources.
Synchronization
causes the
converters in all channels to initiate conversions simultaneously, and can be used to eliminate
sampling skew
between channels.
3.6.1 Sample Rate Control
3.6.1.1 Rate Clock Organization
Sample rates are derived either from an adjustable internal rate generator, or from a single
external hardware clock, as shown in Figure 3.6.1.1. Input channels are arranged into four
groups (Table 3.6.1.1), three of which can be independently designated as either active or
inactive. The sample rate for all channel groups is controlled by the following operations:
a. Assignment to the internal rate generator or to the external clock,
b. Rate generator frequency selection,
c. Rate divisor selection.
The number of channels per group is reduced to four channels for 16-channel boards, or to two
channels for 8-Channel boards. This scheme ensures that the board is divided into four equal
channel groups, regardless of the number of channels present on a board.
3.6.1.2 Rate Generator Assignment
A 4-bit code RATE SOURCE in the Rate Assignments register selects either the internal rate
generator or the external sample rate clock as sample rate source. Group selection codes are
arranged in the register as shown in Table 3.6.1.2-1, and use the assignment codes listed in
Table 3.6.1.2-2.
The Group-0 assignment selects the sample rate source for all groups
,
while Group 1-3 assignments enable or disable the specific channel groups. Disabled groups
do not provide data to the input data buffer.
