User`s guide

24 • Operation Theorem

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 get more accurate measurement 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 the floating signal source. The floating source means it does not have

any connection to real ground. The following figure shows the

single-ended connection. Note that when more than two floating sources

are connected, the sources must be with common ground.

AIN

AGND

n = 0, ..., 15

Floating

Signal

Source

Opertional

Amplifier

To A/D Converter

Input Multipexer

...

Signal Channel Control

There are two ways to control the channel number. The first one is the

software programming and the second one is the auto channel scanning

which is controlled by the ASCAN bit in AD mode control register. As

ASCAN is cleared (0), the value of AD channel MUX register defines the

channel to be selected. Only one channel can be selected in this situation.

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

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

mode, the channel is scanning from channel 0 to the ending channel.

Whenever a trigger signal is rising, 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.

The current A/D channel number could be read back from the A/D data

PCI-9111HR.

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

multiplexer on board. The 4 MSBs could be sent out via the EDO pins of

the CN3 connector to select the external daughter board. At most 16

daughter board can be selected and total 256 channels can be selected

without extra circuits.