User`s guide

Analog Input Boards

Introduction

All boards that have analog input support the cbAIn()/AIn() and cbAInScan()/AInScan() functions, except

expansion boards, which only support cbAIn(). Boards released after the printing of this manual are described

in Readme files contained on the Universal Library disk.

When hardware-paced A/D conversion is not supported, cbAInScan()/AInScan() loops through software

paced conversions. The scan will execute at the maximum speed possible. This speed will vary with CPU

speed. The only valid option in this case is CONVERTDATA.

Concurrent analog input and output for paced analog inputs, paced analog outputs

For boards with both paced analog inputs and paced analog outputs, concurrent analog input and output scans

are supported. That is, these boards allow operations with analog input functions (cbAInScan/AInScan() and

cbAPretrig/APretrig) and analog output functions (cbAOutScan/AOutScan()) to overlap without having to

call cbStopBackground()/StopBackground() between the start of input and output scans.

Trigger support

Digital trigger

If trigger support is "Polled gate" (as opposed to "Hardware"), you implement a trigger by gating the on-board

pacer. This disables the on-board pacer. The trigger input is then polled continuously until the trigger occurs.

When that happens, the software disables the gate input so that when the trigger returns to its original state, it

does not affect the pacer, and acquisition continues until the requested number of samples has been acquired.

There are two side effects to this type of trigger:

 The polling portion of the function does not occur in the background, even if the BACKGROUND option was

specified (although the actual data acquisition does).

 The trigger does not necessarily occur on the rising edge. Acquisition can start at any time after the

function is called if the trigger input is at "active" level. For this reason, it is best to use a trigger that goes

active for a much shorter time than it is inactive.

Similar to ‗Polled gate‘ triggering is ‗Polled digital input‘ triggering, where the pacer is disabled while the

state of a digital input is polled. When the state changes to active, the pacer is enabled by the software. The

polled digital input trigger type limitations are very similar to the polled gate type explained above.

Analog trigger

You set up the trigger levels for an analog trigger using the function cbSetTrigger / SetTrigger, and passing

the appropriate values to the HighThreshold and LowThreshold arguments.

For most boards that support analog triggering, you can calculate the HighThreshold and LowThreshold

values by passing the required trigger voltage level and the appropriate Range to the cbFromEngUnits /

FromEngUnits function.

However, for some boards, you must manually calculate HighThreshold and LowThreshold. If a board

requires manual calculation, that information will be included in the Trigger information for the specific

product in this section. The procedure for manually calculating these values is detailed in the Universal

Library Function Reference in the description of the cbSetTrigger / SetTrigger function.