Standard connection to a Pick-to-Light system

In this article you will learn how to implement a standard connection to a Pick-to-Light system. We not only explain the general mechanisms, but also show the details and examples of the connection. After an email registration we will send you a complete documentation of our standardPick-to-Light interface.

How is the standard connection of a Pick-to-Light system realized?

The connection of a Pick-to-Light system is realized via two separate channels with TCP/IP sockets. The connection is made via software that is installed on a server or PC. One channel is established in each communication direction. The first connection is responsible for switching on the displays. The second interface reports back the acknowledgements of the withdrawals, the quantity corrections and the special keys.

The two channels operate independently (asynchronously). The higher-level warehouse management system can activate or switch off the displays at any time or change the displayed content or colors. Feedback is provided exclusively on the second channel.

Securing the data transmission

To secure the data transmission, an acknowledgement of receipt is sent by the receiver on each data channel (short acknowledgement). If the sender receives the acknowledgement of receipt from the receiver correctly, the telegram is thus considered to have been transmitted.

If the transmitter does not receive an acknowledgement of receipt, the data channel is closed, reestablished and the telegram is repeated.

The telegram counter

Each data telegram is identified by the transmitter in the telegram header with a four-digit telegram counter (0001-9999). The telegram counter is used to synchronize the transmission and reception confirmation of the data telegrams. The receiver always confirms the receipt of a data telegram with the same telegram counter.

After the system start, the transmitter generates a telegram counter with the number 0001. The telegram counter is incremented with each data telegram and increased by +1.

After an overflow above 9999, the telegram counter is reset to 0001 by the transmitter.

The live telegrams

To check the status of the connection, the sender sends the receiver a live telegram (special telegram) without content. The telegram counter is always 0000.

The live telegram is only sent if no active telegrams have been sent in the channel within a certain time (usually approx. 30 seconds). The live telegram is acknowledged normally by the receiver (acknowledgement of receipt).

If the transmitter does not receive an acknowledgement of receipt from the receiver, the connection is closed by the transmitter and reopened. If the receiver does not receive live telegrams from the transmitter, it also reinitializes its connection channel.

Who establishes the TCP/IP connection?

As a rule, the sender always establishes the connection. From this point of view, the first data channel (activation and updating of the displays) is established by the warehouse management system as a TCP/IP client. In that case, the Pick-to-Light system is a TCP/IP server.

The Pick-to-Light system actively establishes a connection to the warehouse management system as a TCP/IP client for the feedback messages. In this case, the warehouse management system is a TCP/IP server.

The two connections are kept permanently open and are only closed in the event of interface malfunctions or system shutdown.

In some situations the connection of a warehouse management system is possible only as TCP/TP client. In that case the Pick-to-Light system works as TCP/IP socket server on both channels. The type of connection is configurable in our Pick-to-Light system.

What controls the standard interface?

Via the standard connection, a warehouse management system (WMS) can switch on, update and switch off the Pick-to-Light displays. The order picker's acknowledgements are reported back to the higher-level system.

In the standard interface, the entire logic of order control, operation and flow is controlled by the warehouse management system.

Here, the response times of the warehouse management system are crucial. The response times here should not exceed 500 milliseconds.

If the process is to be controlled directly by the Pick-to-Light system, the data transfer is implemented differently. Read more about this in a separate article about the customer-specific connection of the Pick-to-Light system.

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