The Casio FX-850P is a scientific calculator introduced in 1987 and sold until 1999. 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 1.228 MHz. 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 batteries as main power supply 1x 3V CR1220 lithium battery as memory backup (RAM power supply) User's manual at http://www.usersmanualguide.com/casio/calculators/fx-850p The calculator had a BASIC interpreter, MEMO function, a formula library. The built-in 8 kB memory could be expanded using the optional Casio RP-8 (8 kB) or RP-33 (32 kB) RAM expansion modules. An optional Casio FA-6 interface board provided a cassette tape recorder connector, a Centronics printer connector and an RS-232C port. The calculator could print data and listings on any Centronics printer; printing graphics required the Casio FP-100 plotter-printer. Later, Casio released the FX-880P, which had 32 kB built-in memory. With a RP-33 expansion module, this model could be upgraded to a total of 64 kB. The memory layout is: 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-P9) 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