Nova

Non-volatile RAM and Real Time Clock (RTC) for Amstrad CPC.

The NVRAM is primarily intended as a debugging tool for developers.

The real-time clock can be used by filesystem/mass storage to set the correct file creation or modification dates.

All Nova cards come with the 32KB chip. Source

Ports

The interface uses only one port (&FE82) to map the NVRAM in and out. It is possible to map it at any address multiple of &2000.

The NVRAM, when it is enabled, masks 8K of RAM or ROM and replaces it with its own contents. Four NVRAM pages of 8K are available.

In the fourth page, the last 8 bytes are not normal RAM, but can be used to read and write the time from the realtime clock.

Assuming the interface is mapped at 6000-7FFF:

Address	Data								Function	Range (BCD)
Address	D7	D6	D5	D4	D3	D2	D1	D0	Function	Range (BCD)
7FFFh	10 Years				Year				Year	00-99
7FFEh	0	0	0	10 M.	Month				Month	01-12
7FFDh	0	0	10 date		Date				Date	01-31
7FFCh	0	FT	CEB	CB	0	Day			Century/ day	00-01/01-07
7FFBh	0	0	10 hours		Hours				Hours	00-23
7FFAh	0	10 minutes			Minutes				Minutes	00-59
7FF9h	ST	10 seconds			Seconds				Seconds	00-59
7FF8h	W	R	S	Calibration					Control

Legend:

CB = CENTURY bit
CEB = CENTURY ENABLE bit (when CEB is set to '1,' CB will toggle from '0' to '1' or from '1' to '0' at the turn of the century)
FT = FREQUENCY TEST bit (must be set to '0' upon power for normal operation)
0 = Must be set to '0'
ST = STOP bit ('1' stops the oscillator)
Calibration (The oscillation rate of any crystal changes with temperature. The accuracy is greatly improved by properly setting the calibration bits)
S = SIGN bit ('1' indicates positive calibration, '0' indicates negative calibration)
R = READ bit
W = WRITE bit

The Nova RTC is supported by all the big guns: FutureOS, SymbOS, UniDOS, HDCPM, etc..

And it can be accessed directly from BASIC. No RSX required.