CPU 221 — what it handles in a panel
The 6ES7211-0AA22-0XB0: It draws 3 A max at 40 °C, so the panel supply needs headroom above the CPU alone — the 24 V bus must carry the CPU plus any expansion modules or field devices on the same circuit. Programming options cover FBD, LAD, and STL. The CPU executes a free cycle (OB 1), interrupt control, and time-controlled processing from 1 to 255 ms.
Integrated I/O and communications
The CPU 221 carries 6 digital inputs and 4 digital outputs. Inputs are source/sink configurable per group, with two high-speed counters (30 kHz each) on E 0.0 to E 0.5. Outputs include two pulse-train outputs (Q0.0 to Q0.1) with a 2 µs rise time, useful for stepper or servo pulse-direction control without an external motion module. The integrated RS-485 port supports PPI and MPI protocols. PPI handles program upload/download and HMI links (TD 200, OP) at 9.6/19.2/187.5 kbit/s. MPI allows data exchange with other S7-200 CPUs, OPs, and TDs at the same rates.
Retentive data and backup
Program and DB 1 are stored on integral EEPROM — no battery needed for the program. Current DB 1 values, retentive memory bits, timers, and counters are buffered by a high-performance capacitor, giving a minimum 8 h backup at 40 °C and up to 50 h. An optional battery module extends retention to 200 days typical. For a furnace thermal profile that must survive a power dip without reloading the recipe, the capacitor backup covers a shift change; the battery covers a weekend.