CPU 221: fixed I/O count for small-machine control
The Siemens 6ES7211-0AA21-0XB0 is a SIMATIC S7-200 CPU 221 compact unit with a DC power supply, 6 digital inputs (DC) and 4 digital outputs (DC). It carries 4 KB of code memory and 2 KB of data memory — enough for ladder logic controlling a small indexing table, a pick-and-place gripper, or a simple conveyor section where the I/O count is fixed and expansion is not needed.
Integration note: DC supply, fixed footprint
The CPU 221 runs on a 24 VDC power supply — the 6 DC inputs and 4 DC outputs are all at the same potential, so no separate field-side supply is needed for the I/O.