PEP Modular Computers Modular Computers RS485 - Page 75

SMART I/O User’s Manual
©1996 PEP Modular Computers GmbHMarch 12, 1996 Page 2 - 35
2
Chapter 2 SMART-BASE
O_START_COUNTER : This call starts the counter; it’s syntax is as follows :
<RetVar> := OPERATE(<iovar>, O_START_COUNTER, <null>);
where the <iovar> is typically t_in.
O_READ_COUNTER : With this call the contents of the counter register
may be read. When this call is issued, the counter is
stopped, it’s register read and then restarted. If a
high-frequency input exists then pulses may be lost
(not counted). The same effect may also be true due
to timeslicing during timer stop and start operations.
Therefore it is recommended that this call be only
used for low frequency inputs (<1kHz). There is no
detection for counter overflow and the call should
not be used for count down operations or square
wave generation. It’s syntax is as follows :
<RetVar> := OPERATE(<iovar>, O_READ_COUNTER, <null>);
where the <iovar> is typically t_in.
O_STOP_COUNTER : This call stops the counter counting up or down and
square-wave generation and has the following
syntax :
<RetVar> := OPERATE(<iovar>, O_STOP_COUNTER, <null>);
where the <iovar> is typically t_in.
The counter/timer is configured automatically as MODE10 (refer to the ‘C’
Programming section) and from within ISaGRAF there is no ability to alter
this configuration.