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the

SCANSetTriggerOut()

function. In the following diagram, TRIG_out level corresponds to the circuit in figure

3.3.

Figure 4-4

The trigger input maybe set for polarity and be enabled or disabled.

4.2.2 Trigger Input

The trigger input line,

TRIG_in

, maybe set for a positive or negative polarity using the

SCANTriggerInState()

command. Under normal operation, the

TRIG_in

line has no effect on the operation of the scanner. It maybe used

to synchronize other test equipment such as in the Triggered Auto Scan and Triggered Scan, where an external
event initiates scanning operation. The level of the

TRIG_in

line maybe monitored using the

SCANGetTriggerIn()

command.

4.2.3 Auto Scan Operation

This operation requires that the Scanner be in one of the following configurations:

TwoWire

FourWire

SixWire

TwoGroups,

FourGroups

. The Auto Scan operation is a software initiated Scan sequence. Issuing

SCANAutoScan()

command triggers an automatic scanning operation, in which the first channel from the first

location in the Scan List table is selected first, followed by a delay equal to t-Step. Channels are selected
sequentially from the Scan List. The total number of points in the scan is controlled by the

iPoints

parameter passed

by the

SCANAutoScan()

function, which must be a value between 1 and 192. This mode maybe terminated by

sending

SCANAbort()

command to the Scanner during the scan. Use the

SCANOpenAllChannel()

function at the

end of the scan, if you wish to open the last selected channel. The Trigger output signal can be used to synchronize
other instruments to the SM4000 Scanner. The value of

t-Step

and t-Actuation

can be set to generate a trigger output

signal for triggering instruments. For instance, setting the TRIG_out polarity to positive sense (as in Figure 4-6) will
result in a positive edge to trigger an SM2044 DMM, after a channel relay is closed and settled.

Figure

4-6.

AutoScan is a software-initiated channel scanning procedure.

4.2.4 Triggered Auto Scan Operation

This operation requires that the Scanner be in one of the following configurations:

TwoWire

FourWire

SixWire

TwoGroups,

and

FourGroups

. The Triggered Auto Scan operation is a hardware-triggered version of the above

Auto Scan operation. The trigger polarity can be selected. The

SCANTrigAutoScan()

function sets the Scanner

into the Triggered Auto Scan mode, in which the Scanner waits for a trigger edge to initiate an Auto Scan operation.
Once a trigger is received, the first channel from the first location in the Scan List table is selected, followed by a
delay equal to

t-Step

, then the selection of subsequent channels as specified in the Scan List table. The Scanner

proceeds to sequentially select a total of

iPoints

. The last parameter is passed to the scanner by the

SCANTrigAutoScan()

function. This value must be between 1 and 192. This may be terminated by sending

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