Casio FX-850P

The Casio FX-850P is a scientific calculator.

Technical specifications

* 2 lines with 32 5×7 characters LCD
** (some indicators and a 5 digit 7-segment display)
* 8 KB RAM (FX-860P: 24 KB, FX-880P: 32 KB)
* CPU: VLSI at 1,228MHz. Hitachi HD62002A01 (FX-860P, FX880P: HD62002A03)
* Integrated speaker
* Internal slot for memory expansion (32 KB)
* Connector with support for RS232 and centronics (only level converter for RS232, centronics needed)
* LCD Driver: 2 x HD66100F
* 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 32 KB as a standard. This model could be upgraded to a total of 64 KB.

The memory layout is as follows:
* 0000-00FF Screen memory
* 0100-01FF Reserved for internal functions
* 0200-02ff INPUT Buffer
* 0300-03FF CALCJMP, VALF Buffer
* 0400-04FF Reserved for IN/OUT/CALC modes (CALC$)
* 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.

Any function in the library can be executed from a regular BASIC program by using GOTO "LIB0:NNNN" where NNNN is the function number (e.g. 5010 for prime factorization). The command "GOTO LIB0:0400" executes a self-test program.

Characters 252 to 255 were user defined. They could be defined by issuing the command DEF CHR$(n)="HHHHHHHHHH" where n ranges from 252 to 255 and the H's are 10 hexadecimal digits (5 bytes). Every byte defines the pixel pattern for a column. Since a column is 7 pixels high, the least significant bit of every byte is ignored.

The CHR$(26) would activate a different character set for Katakana and Kanji characters. CHR$(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.

External links

* [http://mycalcdb.free.fr/main.php?l=0&id=398 Casio FX-850P] on [http://mycalcdb.free.fr MyCalcDB] (database about '70s and '80s pocket calculators)