User`s guide

Operation Theory • 35

Analog Input Signal Connection

The PCI-9111 provides 16 single-ended analog input channels. The analog

signal can be converted to digital value by the A/D converter. To avoid ground

loops and to obtain accurate measurements of A/D value, it is quite important

to understand the signal source type. The single-ended mode has only one

input relative to ground and is suitable for connecting with a floating signal

source. A floating source means it does not have any connection to a real

ground. The diagram below shows a single-ended connection. Note that when

more than two floating sources are connected, the sources must have a

common ground.

Figure 10. Analog Input Signal Connection

Signal Channel Control

There are two ways to control the channel number, either by a software

program or by auto channel scanning which is controlled by the ASCAN bit in

the AD mode control register. As ASCAN is cleared (0), the value of the AD

channel MUX register defines the channel to be selected. Only one channel

can be selected in this situation.

When ASCAN is set (1), the value in the AD channel MUX register defines the

ending channel number of the auto-scanning operation. Under auto scan

mode, the channels are scanned from channel 0 to the ending channel.

Whenever a trigger signal is on the rising edge, the channel number to be

selected will increase automatically. For example, if the ending channel

number is 3, the auto channel scanning sequence is 0, 1, 2, 3, 0, 1, 2..., until

the ASCAN bit is cleared.

Note the current A/D channel number can be read back from the A/D data

PCI-9111HR.

Note that the MUX register is 8 bits long. The 4 LSB is used to select the

multiplexer on board. The 4 MSB can be sent out via the EDO pins of the CN3

connector to select an external daughter board. At most 16-daughter boards

can be selected and a total of 256 channels can be selected without extra

circuits.

AIN

AGND

n = 0, ..., 15

Floating

Signal

Source

Opertional

Amplifier

To A/D Converter

Input Multipexer

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