PLC Programming: PROGRAM UPLOAD vs PROGRAM DOWNLOAD
Introduction
Upload and download refer to the processes of transferring a program and related data between a personal computer (PC) running programming software (e.g., GX Works2 or GX Works3) and a Programmable Logic Controller (PLC). Collectively, these operations enable the exchange of control logic, parameters, and configurations to manage, update, or retrieve the PLC’s operational program.
This is a controversial topic as it causes confusion, however the definitions of these actions (upload and download) will shed light on why these terms are used as they are:
Download :
Definition : The process of transferring data from a passive recipient to an active initiator, where the active initiator requests or pulls the data to itself.
Explanation : In a download, the entity initiating the transfer (active initiator) retrieves data from another entity (passive recipient) that holds or provides the data. The data flows toward the initiator, which is actively seeking to acquire it.
Upload :
Definition : The process of transferring data from an active initiator to a passive recipient, where the active initiator sends or pushes the data to the recipient.
Explanation : In an upload, the entity initiating the transfer (active initiator) sends data to another entity (passive recipient) that accepts or stores the data. The data flows away from the initiator, which is actively transmitting it.
Upload (Read) PLC programs FROM PLC to PC.
Upload : This refers to transferring a PLC program from the PLC to the PC. Think of it as “retrieving” or “reading” the program from the PLC’s memory into the programming software.
- Purpose : To retrieve the existing program running on the PLC, often for troubleshooting, documentation, backup, or modification.
- Example : You’re working on a machine with a PLC, but you don’t have the latest program file on your PC. You upload the program from the PLC to view or edit it.
https://www.bpx.co.uk/dbdocument/121610/gx%20developer%20usermanual.pdf p.18-1
In GX Works… Uploading (Read):
Download (Write) PLC programs FROM PC to PLC.
Download : This refers to transferring a PLC program from the PC (where the programming software resides) to the PLC. Think of it as “sending” or “writing” the program to the PLC’s memory.
- Purpose : To update or install a new program, configuration, or firmware on the PLC so it can execute the desired logic.
- Example : You’ve written or modified a ladder logic program on your PC using the programming software, and you want to load it onto the PLC to run the process.
https://www.bpx.co.uk/dbdocument/121610/gx%20developer%20usermanual.pdf p12 -1
In GX Works… Downloading (Write):
Conclusion
Downloading (or “Write to PLC”) sends the program from the PC to the PLC, while uploading (or “Read from PLC”) retrieves the program from the PLC to the PC, facilitating programming, maintenance, and troubleshooting of industrial automation systems.
