41CL Calculator Manual
© 2019 Systemyde International Corporation
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FORTH ROM visible. The way around this problem is to disable the MMU during
programming. The sequence of commands shown below will enable FORTH ROM.
First, the MMU is disabled. This has no effect on the contents of the MMU:
XEQ ALPHA
MMUDIS
ALPHA
Next, the MMU for pages 4 and 7 are programmed to point at the FORTH ROM image:
ALPHA
804040-809A
ALPHA
XEQ ALPHA
YPOKE
ALPHA
ALPHA
804070-809B
ALPHA
XEQ ALPHA
YPOKE
ALPHA
Finally, the MMU is re-enabled:
XEQ ALPHA
MMUEN
ALPHA
Disabling the FORTH ROM is only possible by turning off the calculator and
momentarily removing the batteries, because once the FORTH module is active the
41CL
Extra Functions
are no longer available.
The HP Service ROM
The HP Service ROM was used by HP to test returned calculators, and is hard-coded to
use Page 4. This ROM is intended to take over the calculator, so installation is as simple
as programming the MMU for Page 4. Refer to the HP 41C Service Manual for
instructions on using the test facilities in this ROM.
ALPHA
804040-8004
ALPHA
XEQ ALPHA
YPOKE
ALPHA
Disabling the HP service ROM is only possible by turning off the calculator and
momentarily removing the batteries, which disables the MMU.