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GW EIP/ASCII...
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PHOENIX CONTACT 3785_en_B
6.7 Receive communication methods
The GW EIP/ASCII... transfers received data to a MicroLogix, SLC, and PLC-5 controller
using the “Write to Tag/File” or “Polling” option.
6.7.1 Write to Tag/File - Unsolicited message
The “Write to Tag/File” option requires the least amount of programming and is the
recommended method to transmit data to a controller. When the GW EIP/ASCII... receives
a serial or socket packet, the data packet is immediately written to a file data location on the
PLC.
The “Receive Data File” name must be the same file name and offset defined to receive data
on the PLC. The file on the PLC must be of integer type and must be of sufficient size to
contain the sequence number, length, and data field associated with the maximum sized
received data structure. The sequence number is incremented when new data is received.
The “Maximum PLC Update Rate” setting may need to be increased in order to ensure the
PLC program processes the data before the message is overwritten by the next incoming
message.
6.7.2 Polling
The “Polling” option allows the PLC to periodically request data from the GW EIP/ASCII....
The serial or socket data is returned in the response to the data request message.
The file on the PLC must be of integer type and must be of sufficient size to contain the
sequence number, length, and data field associated with the maximum sized received data
structure. New data is indicated with an incremented sequence number. The same data
may be returned more than once. However, the same data packet also returns the same
sequence number. No data is indicated with a length of zero. While the GW EIP/ASCII...
queues received serial port data, the PLC program must poll for new data faster than the
data can be received on the serial port to ensure the receive queues on the GW EIP/ASCII...
do not overflow. For example, if two packets can be received per second on the serial port,
then the polling rate would need to be at least once every 500 ms.