Casio FX-850P

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The Casio FX-850P is a scientific calculator.

[edit] Technical specifications

2 lines with 32 5×7 characters LCD
- (some indicators and a 5 digit 7-segment display)
8 KB RAM
Integrated speaker
Internal slot for memory expansion (32 KB?)
Connector with support for rs232 and centronics (only level converter for rs232 needed)
(only latch for centronics needed)
2x 3V CR2032 lithium as power supply
1x 3V CR2012 lithium as RAM power supply

You can find a user's manual at: http://www.usersmanualguide.com/casio/calculators/fx-850p

This was a very popular calculator in the '90s 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 useful was the build in formula library.

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

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

The memory layout is as follows:

0000-00FF Screen memory
0100-02FF Reserved for internal functions
0300-0307 Reserved for 4 custom characters (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

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

A few glitches are:

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 programmed in BASIC itself and could be extracted with a BASIC decompiler.

Characters 252 to 255 where user defined and the CHR$(26) would activate a different character set for Kanji character. CHR$(27) would deactivate Kanji.

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

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