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By switching off the screen, the Blink doesn't read the font bit maps in OZ ROM, and the Flash chip can be in command mode without being disturbed by the Blink.
Important:
INTEL I28Fxxxx series Flash chips require the 12V VPP pin in slot 3 to successfully blow data to the memory chip. If the Flash Eprom card is inserted in slot 1 or 2, this routine will report a programming failure. It is the responsibility of the application (before using this call) to evaluate the Flash Memory (using the OS_Fep, A=FEP_CDID call) and warn the user that an INTEL Flash Memory Card requires the Z88 slot 3 hardware, so this type of unnecessary error can be avoided. Equally, the application should evaluate that saving to a file that is on an UV Eprom only can be performed in slot 3. This routine will report failure if saving a file to slots 0, 1 or 2.