As you can see in this photograph, not all slots in this particular rack are occupied by I/O cards either:
Each discrete I/O card has indicator LEDs showing the on/off status of each I/O bit, and the analog card has a single LED showing that the card is powered.Ī nine-slot SLC 500 system is shown in the next photograph, controlling a high-purity water treatment system for a biopharmaceuticals manufacturing facility. The processor card has LED indicators for “Run” mode, “Fault” conditions, “Force” conditions (when either input or output bits have been forced into certain states by the human programmer for testing purposes), and communication network indicators. The slots 5 and 6 hold discrete output and analog output cards, respectively.Ī feature visible on all cards in this system are numerous LED indicators, designed to show the status of each card. The slots 3 and 4 are empty (revealing the backplane circuit board and connectors for accepting new cards). The first three slots of this particular SLC 500 rack (0, 1, and 2) are occupied by the processor card, an analog input card, and a discrete input card, respectively.
