What this S7-200 CPU 221 does in a panel
The Siemens 6ES7211-0BA22-0XB0 is a S7-200 CPU 221, the smallest fixed-I/O member of the S7-200 family, designed for standalone control of small machines or as a remote I/O node on an MPI or PPI network. It carries 6 digital inputs (sink/source configurable per group) and 4 relay outputs rated for 200 W on lamp load with AC, or 30 W on DC — enough to switch contactors, solenoid valves, and indicator lamps directly without interposing relays. The CPU runs on a 100 V AC to 230 V AC supply, with the 24 V DC sensor supply drawn from the same power rail, so it fits panels where a separate 24 V power supply is not already present.
Programming and protocol support
Programming is done in LAD, FBD, or STL via Siemens STEP 7-Micro/WIN software; the instruction set covers bit logic, timers, counters, integer and floating-point math, and communications instructions. The integrated RS 485 interface supports PPI protocol for programming and HMI communication (TD 200, OP) at 9.6/19.2/187.5 kbit/s, and MPI protocol for data exchange with S7-300/S7-400 CPUs and operator panels at 19.2/187.5 kbit/s. Program memory is 4 KB, stored maintenance-free on integral EEPROM; data in DB 1 is also EEPROM-backed, while current values, retentive bits, timers, and counters are buffered by a high-performance capacitor (50 h backup typical, 8 h minimum at 40 °C) or an optional battery module for up to 200 days.
Input and counting capability
The 6 digital inputs accept 2-wire sensors, with signal '0' at 0 to 5 V and signal '1' at minimum 15 V, making them compatible with most 24 V DC proximity switches and pushbuttons. Four high-speed counters (30 kHz each, 32-bit including sign) can be used as up/down counters or to connect two incremental encoders with 90° phase-shifted pulse trains at up to 20 kHz, with parameterizable enable/reset and interrupt on setpoint reach. The CPU also includes 256 timers: 4 timers covering 1 ms to 30 s, 16 timers covering 10 ms to 5 min, and 236 timers covering 100 ms to 54 min — enough range for most machine-cycle timing without an external timer module.
The RS 485 port supports shielded cable runs up to 500 m and unshielded up to 150 m, so the CPU can be located at the machine rather than in a central cabinet. Operating humidity range is 5 % to 95 % RH (class 2 per IEC 1131-2), and the unit dissipates 6 W typical — no forced cooling needed in a standard IP20 enclosure.
This is the original S7-200 CPU 221 variant with the 22XB0 firmware version; it is still supported by STEP 7-Micro/WIN and remains a common spare part for installed S7-200 systems.