CV x CX hardware differences ?


Anyone knows what are the hardware differences between HP-41CV and CX ?
I know that there is a different ROM and more RAM. What I do not know is, how are implemented the TIME functions. Is there any dedicated timekeeping chip ? If not, how is the time maintained when the calculator is switched off ?
Is it possible to find some documentation about it ?

Thx for any help


Yes there is a timekeeping real-time-clock chip. In the fullnut CX it's the 20 pin chip at the edge of the logic board closest to the + key (that's clearer than saying 'left' or 'right' :-)). It's a
1LF6 IIRC. The other differences are the extra RAM (for extended memory), the extra ROM (time functions, extended functions and the extra CX-only functions) and the main ROMs contain different code (to support the extra ROMs)
The extedned function ROM is not the same as that in an extended functions module. It sits in page 3 for one thing, where a CV main ROM would not look for it.
In the case of the halfnut 41, there's a PCB mounted across the main CPU chip containing the CX-specific stuff (timer chip, extended RAM, extended function/time ROMs). But the main ROMs (in the halfnut
display driver) are diffferent as well for the reason I've just specified. Which meas that if you add the PCB to a halfnut CV, it finds the time ROM and time chip but _not_ the extended functions ROM. You can't upgrade a halfnut CV to a CX like that, alas.


Thx for the informations.
Is there some documentation about the CX hardware and/or the timekeeping chip ?
The reason why I am asking is, that I am trying to design the "spare parts". I would like to be able to emulate the functions of the old HP ICs with modern FPGAs and microcontrollers. When the effort will be finished, I will put the whole design in public domain.

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