Figure
4-7.
Positive edge Triggered AutoScan is a hardware initiated automatic scanning process.
4.2.5 Triggered Scan Operation
This operation requires that the Scanner be in one of the following configurations:
TwoWire
,
FourWire
,
SixWire
,
TwoGroups,
and
FourGroups
. The Triggered Scan operation is a hardware driven scanning process. Each step
through the Scan List table is initiated by hardware trigger event. The trigger input signal edge polarity can be
selected. The
SCANTrigScan()
function sets the Scanner into the Triggered Scan mode, in which the Scanner
expects a total of
iPoints
triggers. Once this command is issued to the Scanner, it waits for the first trigger edge to
select the first channel from the first location in the Scan List table. Following the selection of each point, the
Scanner waits for t-Actuation period, during which triggers are ignored. The Scanner responds to subsequent trigger
edges by sequentially selecting channels stored in the Scan List. The total number of points in the scan is controlled
by the
iPoints
parameter passed to the scanner by the
SCANTrigScan()
function, which must be a value between 1
and 192. This mode is concluded at the end of the number of points specified, or terminated by sending
SCANAbort()
command to the Scanner. Use the
SCANOpenAllChannel()
function if you wish to open the last
selected channel.
Figure 4-8. Positive edge Triggered Scan operation is a hardware initiated scanning process.
4.2.6 Single Step Scan Operation
This operation requires that the Scanner be in one of the following configurations:
TwoWire
,
FourWire
,
SixWire
,
TwoGroups,
and
FourGroups.
The Single Step Scan operation is similar to the Triggered Scan process with the
exception that each step through the Scan List table is initiated by the
SCANStep()
command rather than by
hardware trigger event. The
SCANSetupStep()
function prepares the Scanner for this operation by resetting the
Scanner’s Scan List pointer to point to the first entry of the table. In response to the
SCANStep()
command, the
Scanner selects the channel stored in the Scan List location pointed to by the Scan List pointer, then it increments
this pointer to point to the next location. The number of points in the scan is controlled by the number of times
SCANStep()
commands is issues since the last
SCANSetupStep()
function was executed. When done using the
SCANStep() and SCANSetupStep()
functions, the Scanner is going to remain with the last channel selected. The
maximum number of entries in the Scan List is 192. The polled version of
SCANStep()
,
SCANStepCmd()
function
maybe used if a polled control is required. Read about the usage of polled operations in the “Polled Type
Operations” section. Use the
SCANOpenAllChannel()
function if you wish to open the last selected channel.
Signametrics
22
