The LED display is located on the front panel of the CPU:
LED Indication Related to Firmware Update
LED Indicator
Description
DL (download)
Blinking: Firmware update in progress.
OFF: No firmware update in progress.
CPU
(central processing unit) The CPU, also known as the processor or controller, is the brain of an industrial manufacturing process. It automates a process as opposed to relay control systems. CPUs are computers suited to survive the harsh conditions of an industrial environment.
