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4
USING THE /260+
This chapter describes the various hardware operations associated with implementing the user’s
application. Programming operations are discussed in the Amplicon ADIO driver manual
elsewhere on the SOFTMAN CD ROM. Details of the registers and software are given in chapters
5 and 6 respectively.
Reference should also be made to chapter 2 ‘Getting Started’ and chapter 3 ‘Making the
Connections’ before implementing any of the described operations.
4.1
Analog Inputs
There are 16 channels of analog input and these are designated channel numbers 0 through 15
(Ch0 to Ch15). The signal on the addressed channel is selected by the multiplexer, internally
normalised by the gain stage and applied to the Analog to Digital Converter (ADC) input for
conversion to digital form.
In differential mode eight differential inputs are formed from adjacent pairs of input channels.
It is important that no input voltage is allowed to exceed the limits of the input protection circuitry,
i.e. input voltage must not exceed ±20 V dc.
The digital data available from the ADC is a 16-bit conversion result. See Figure 4-3, for a
description of the ADC output codes.
4.2
Analog Input Voltage Range
The input voltage range is established by the gain setting of the analog amplifiers preceding the
ADC. The voltage range is set by means of software.
Unipolar input
voltage range
Bipolar input
voltage range
±10
0-10
±5
0-5
±2.5
0-2.5
±1.25
FIGURE 4-1
INPUT VOLTAGE RANGES
4.3
Analog Input FIFO
Samples taken by the ADC are passed to a 4096 sample first in first out (FIFO) memory. This
means that the card can store samples locally and interrupt the host PC when there are enough
samples to be collected. This reduces the load on the processor as data transfers over the PCI
bus are much faster when multiple samples are transferred.
More importantly, when running under multi-tasking operating systems such as Windows NT, 95,
98, 2000 & XP, response to interrupts may be very slow. If the processor is busy on a different
task at the time an interrupt comes from the /260+ it may take considerable time before
the interrupt is serviced.
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