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Casio FX-850P

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The Casio FX-850P is a scientific calculator.

Technical specifications

  • 2 lines with 32 5x7 characters LCD
    • (some indicators and a 5 digit 7-segment display)
  • 8 kb RAM
  • Integrated speaker
  • Internal slot for memory expansion (32kb?)
  • connector with support for rs232 and centronics (only level converter for rs232 needed)
  • (only latch for centronics needed)
  • 2 3V CR2032 lithium as power supply
  • 1 3V CR2012 lithium as RAM power supply
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This was a very popular calculator in the 90ies at any university.

It had a BASIC interpreter, which was very easy to use, as well as a MEMO function, which allowed the user to insert text. This was fully used by students to cheat on exams.

Very usefull was the build in formula library.

The calculator could have its memory expanded to a total of 40KB using the option RP-33 expansion (8KB + 32KB).

Later, Casio released the FX-880P, which had 32KB as a standard. This model could be upgraded to a tota of 64KB.

The memory layout was this:

0000-00FF Screen memory

0100-02FF Reserved for internal functions

0300-0307 Reserved for 4 custom caracters (ASCII 252 a 255)

0308-03FF Reserved for internal functions

0400-04FF Reserved for IN/OUT/CALC modes

0500-074A Reserved for internal functions

074B-0752 Reserved for storing the user PASSWORD

0753-175A Reserved for internal functions

175B-175C Vector pointing to MEMO memory start

175D-1FE4 Reserved for internal functions

1FE5-1FFF Vectors pointing to P0-P9 memory start

2000-9FFF User memory (shared by MEMO and P0-p))

A000-BFFF Repetition of 0000-1FFF

C000-DFFF Repetition of 0000-1FFF

E000-FFFF Repetition of 0000-1FFF

Memoriy area A000-FFFF was either available as user memory (if expansion was present), or would simply repeat the contents of 0000-1FFF

A few tricks where:

POKE 1867,0 -> would delete any user PASSWORD

POKE PEEK(8027)+256*PEEK(8028),32 -> would recover contents of MEMO after a RESET ALL

POKE PEEK(8027)+256*PEEK(8028),26 -> would hide contents of MEMO, much like a RESET ALL would do, but without losing the programs

The internal function library was programed in BASIC itself and could be extracted with a BASIC decompiler.

Caracters 252 to 255 where user defined and the CHR$(26) would activate a diferent caracterset for Kanji character. CHR$(27) would deactivate Kanji.

This calculator also features an interface board, which allows it to contect it to some proprietary devices.

There are many schemes available to make a serial cable to conect the calculator to a PC or to another Casio FX-850P, allowing the transfer o MEMO and stored programs.

Autor: Vitor Martins-Augusto

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