Casio FX-850P

From Wikipedia:

The Casio FX-850P is a scientific calculator introduced in 1987 and sold until 1992.

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 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.