UPD4990: Difference between revisions
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==Interface== | ==Interface== | ||
The [[READ_CALENDAR]] BIOS call can be used to transparently load the uPD4990 time and date to [[ | The [[READ_CALENDAR]] BIOS call can be used to transparently load the uPD4990 time and date to [[BIOS RAM locations]]. | ||
Raw access is done through {{Reg|REG_STATUS_A}} for input and {{Reg|REG_RTCCTRL}} for output. | Raw access is done through {{Reg|REG_STATUS_A}} for input and {{Reg|REG_RTCCTRL}} for output. | ||
==Failure== | |||
A damaged chip, oscillator or their connections provokes the [[Calendar error]] or a freeze on MVS boards. | |||
==Datasheet== | ==Datasheet== | ||
Revision as of 03:53, 31 December 2015
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.
Interface
The READ_CALENDAR BIOS call can be used to transparently load the uPD4990 time and date to BIOS RAM locations.
Raw access is done through REG_STATUS_A for input and REG_RTCCTRL for output.
Failure
A damaged chip, oscillator or their connections provokes the Calendar error or a freeze on MVS boards.
Datasheet
Official uPD4990A datasheet: [[1]]