User`s manual

EM1500 User’s Manual www.rabbit.com 55
Figure 5.9 Polling Tab
The polling facility allows a device attached to an EM1500 serial port to be regularly queried. Polling can
be used to periodically
• collect data from the device and/or
• check the state of health of the device and/or
• tell the device that it is still connected to something.
Polling options are entered under the “Polling” tab for each serial port. It is necessary to check the “Enable
poll” option to enable any polling. When checked, a number of other options become enabled. These
options are described below.
Note that polling is inserted by the EM1500 at arbitrary points (from the point of view of the attached
device or network peer). Thus, if you select the “Poll when connected” option, there may be undesirable
interaction with the normal data stream. In this case, you may want to select some form of packetization
for the connection. If packetizing is in use, then polling only occurs between successive packets. This is
less likely to cause interference. Also, each “send” string in the polling sequence will be sent as a single
packet to the serial port.
Enable poll
Enable device polling sequence. Checking this option makes the rest of the polling
options available.