DFE WebHandler 3 Instruction Manual page 37

Speed and Roll Diameter and allows the user to turn Tension On or Off, and select Manual or
Auto Control Mode to facilitate the process. Standard tuning instructions still apply (see Section
4.4). Remember to STORE your settings when finished.
(6) Using the Host Interface:
The WebHandler
PLCs using its Host Interface. Setpoints, tension modes and other parameters may be sent to the
WebHandler, and tension readings and other status information may be read from it.
The WebHandler, of course, has a local front-panel interface. There is a provision to select
whether the WebHandler will accept input from that interface, or from the Host interface. To
activate the Host interface, go to the Setup Menus group and select the function
SerialCommSource, then select "host", then OK. At that time, the Host interface will activate
but the local interface will remain functional. Control input will continue to be accepted from
the local interface along with the Host. Keep in mind that it is possible for a Host and a User to
be selecting conflicting controls. The unit will follow the last entry.
All commands include a unit address for those applications which have multiple units on a
single RS485 serial communications link. Appendix F contains a listing of these commands. In
the command descriptions, "#" indicates the WebHandler's one-byte ASCII address from 1
through 9 or A through Z. This provides 35 possible addresses for multiple unit installations.
The factory default ("1") is usually satisfactory unless multiple units are to be connected to the
same loop using an RS485 interface. If this is the case, each controller must be assigned a
unique address as follows.
Go to the Setup Menus group and select the function Network Unit ID. Change the address of
each controller to an address different from any of the other controllers. The choices of
addresses are as described above.
Whenever the controller receives a command which requires a specific response to that
command, it responds with a prefix specific to that command, its address, and then the requested
information. In this way the host has confirmation that the WebHandler processed the command
correctly and that the data is valid. If the WebHandler receives a command which only requires
the WebHandler to process the command, the WebHandler still acknowledges receipt of that
command with the ACK (acknowledge) response, "%#A". If the WebHandler receives a
command but does not recognize it, or for any reason cannot process the command, the
WebHandler will acknowledge the receipt of these undefined or inappropriate commands or
command arguments with the NAK (negative acknowledge) response, "%#?".
The host computer may transmit commands to other devices on the same network as the
WebHandler. If the command prefix is not a "$" character, the WebHandler will ignore it
completely, and no NAK response will be generated. In similar fashion, a WebHandler with a
given address will ignore a command sent to a WebHandler with a different address.
In multiple unit installations it may be desirable to broadcast the same command to all
WebHandlers. An example of this would be turn all WebHandlers' tension "On" at the same
time, or to simultaneously update all of them with a new set-point. For this purpose, the address
"0" is reserved as a "broadcast" address. However, to eliminate garbled data from multiple
controllers responding with the ACK response, WebHandlers do not respond when a broadcast
command is issued (this is the only circumstance that WebHandler does not respond to a
command when it is processed correctly). Be aware that other manufacturers products may
respond in different ways, making this usage have unpredictable results.
The user must constrain command arguments, including numeric ranges, to be valid entries,
otherwise unpredictable results may occur.
Note: All host commands and all WebHandler responses below must be followed by the ASCII code for
<CR> (0Dh).
™
3 has the capability of serial communication with external computers or
31