UPD4990: Difference between revisions
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Revision as of 15:27, 26 June 2011
The uPD4990 is a Real Time Clock (RTC) chip made by NEC, to keep the calendar's time and date informations on MVS boards.
It shared the battery-backed RAM's battery and had a separate 32.768kHz crystal clock to run when power was off.
Datasheet
Official uPD4990A datasheet: [[1]]