This feature is used to display images when the calculator is turned OFF.
Single hard-coded OFF image is present in calculator firmware and this image is displayed
whenever the calculator is turned OFF and FAT disk doesn’t contain any valid custom image or the
FAT disk is in error state.
Custom OFF images should be stored in
/OFFIMG/
directory. All valid images are then cyclically
displayed one after each calculator OFF in the order how they appear in
/OFFIMG/
directory.
OFF images require specific image format. It has to be
.bmp
file with dimensions 400 x 240 and 1 bit
depth.
Examples of OFF images can be found on
"A collection of off-screen images"
page.
3.5. RTC correction
Note that to apply RTC correction you have to know (measure and calculate) ppm drift of calculator
clock first.
Use following steps to apply clock frequency correction.
1. Calculate correction factor C which best matches required ppm correction P
C = 2^20 P /(10^6 + P)
resulting value C has to be integer and -511 <= C <= 512.
2. Create file
/rtccalib.cfg
in root directory of calculator FAT disk and write value C there.
3. Once the RTC correction is active the ppm value is written in Setting menu at the end of "Set
Time >" line.
It is possible to use approximate expressions between correction factor C and ppm value P (with
reasonable precision):
C = 1.04858 P
P = 0.953674 C
3.6. Patched mainframe ROMs
Changes to the original NUT-CX.MOD - 30.08.2019, by Ángel M. Martin
Fitting all these into the ROMS wasn’t terribly difficult, although there were numerous restrictions
both in available space and FAT sizes. The ROMS are totally full now..
3.6.1. Patch to routine [MASK]
Needed for ALPHA display of lower-case characters. The Half-nut LCD display is capable of
displaying lowercase chars but the 41CX-OS code wasn’t modified to display them properly in
ALPHA. This patch corrects that.
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