Teenage Engineering PO Modular 16 is a standalone keyboard with 16 keys, tuneable keys, and a programmable 16-slot step sequencer with 4 tracks per slot and 1 pattern per track. It does not output sound; the unit controls the 400 or any other modular synthesizer. It outputs CV, MIDI over 3.5 mm, and trig.

It can store up to 64 independent patterns, each up to 64 steps long.

The 16 slots are labeled 1 to 16, which also correspond to the keys on the keyboard.

The 4 tracks are labeled T1–T3 and TK, where K represents the keyboard. You can connect the CV/gate outputs to other Operator modular units or any other compatible device and use PO Sync to synchronize Pocket Operators (POs), and use the MIDI output to control any MIDI equipment.