UPD4990

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uPD4990 RTC in a (dirty) 1FZS MVS slot.

The uPD4990 is a RTC (Real Time Clock) chip made by NEC, used on MVS boards to keep the calendar's time and date.

It shares the battery-backed RAM's battery and has a separate 32.768kHz crystal clock to run even when power is off.

Datasheet

Official uPD4990A datasheet: [[1]]