CPU 316 — what the 128 KB working memory means for your rack
The Siemens 6ES7316-1AG00-0AB0 is a SIMATIC S7-300 CPU with 128 KB integrated working memory (42 K instructions), expandable up to 512 KB RAM, and 192 KB max integrated RAM. That 128 KB holds the user program and data; the expandable RAM handles additional data blocks or recipe storage without swapping the CPU. Rated 24 V DC supply, it powers up to 4 racks (10 m each) with a max of 128 inputs. The hardware clock (1 s resolution) keeps time stamps consistent across the line — useful for batch traceability in process applications. Execution speeds: 0.3 ms typ for bit operations, 1 ms typ for word operations — adequate for mid-speed discrete control and simple motion sequences in a brewery or distillery CIP skid.
Programming languages and retentive memory
Supports LAD, FBD, STL, SCL (limited), CFC (limited), GRAPH (limited), and HiGraph (limited). That means the same code base written in STL or LAD for older S7-300 projects ports directly; SCL and CFC are available but with constraints — check the specific block limits before committing a complex algorithm. Retentive memory: with battery, 128 KB holds data for 2 years; without battery, 4 KB persists for 10 years. The static area is 4 KB, dynamic 8 KB. For a batch recipe that must survive a power cycle, budget the 4 KB non-battery retentive space or plan for a battery change every two years. Supports MPI communication and STEP 7 programming environment. The integrated software controller via loadable FB allows simple closed-loop logic without an external module.
Lifecycle — EOL hot, sourced to order
If you need a drop-in replacement for an existing S7-300 rack, this is the exact order code; if you are designing a new line, the S7-1500 peer is the forward path.