PM891/PM891k01 ABB PM891/PM891k01 [caption id="attachment_1447" align="aligncenter" width="600"] PM891[/caption] The PM891 processor is a monolithic unit equipped with a power supply, CPU board, and unit terminal. The unit contains a microprocessor and RAM memory, a real-time clock, LED indicators, INIT buttons, and a secure digital interface. The PM891 does not contain any internal battery.