HP-41

The 1979 HP-41 series programmable calculator, which was produced until 1990, and was used in the Space Shuttle missions, has a processor called "Coconut" (or 1LE3 CPU), RAM, ROM, I/O, and uses the interpreted programming language FOCAL ("Forty One Calculator Language"). The operating system and the interpreter are stored in ROM, and were programmed using the Coconut processor assembly language also called MCODE (or "M-Code").

What catches my attention most about this calculator are the hardware expansion slots that allow you to add additional components to the system, expanding its capabilities by adding new devices, a predecessor to the expansion slots found in modern computers.

Although it lacks the processing power and versatility of modern laptops, the HP-41's design philosophy of portability and user customization influenced the development of more advanced portable computing devices.

• HP-41C, at wikipedia.org .
• HP-41 Library, at hp1.org .
• A_programmers_handbook_v.2.07, by Poul Kaarup, 2015.
• CPU Detailed Description, by Hewlett-Packard, 1981.
• Schematic, Hewlett-Packard, 2000.
• ROM listing
  • http://www.hp41.org/LibView.cfm?Command=View&ItemID=1064
  • http://www.hp41.org/LibView.cfm?Command=View&ItemID=304
• Monte Dalrymple's "Inside the NUT CPU" - provides an in-depth look at the Nut CPU, which is the central processing unit of the HP-41 calculator series. It delves into the architecture, design, and functionality of the CPU.
• Doug Wilder´s "QuinTable.pdf" - HP-41 microcode table, the low-level instructions that control the operations of the HP-41 calculator series.
• David's assembler manual - comprehensive guide that provides detailed instructions on how to use the assembler software for programming the HP-41.
• Monte Dalrymple's "NEWT Microprocessor Technical Manual" - the NEWT (Nut, Expanded, With Turbo) CPU is an upgraded version of the Hewlett-Packard Nut microprocessor, which was employed in a number of HP calculators, including the HP-41 series.
• Ken Emery's "HP-41 MCODE For Beginners" - MCODE is the internal machine code used by the HP-41, one level below the set of "user code" instructions that users and programmers are accustomed to dealing with. Some user code instructions like CLX are implemented by the HP-41 in just a few MCODE instructions; other user code instructions like TAN consist of hundreds of MCODE operations.
• HP-41 IC Specifications
  • https://literature.hpcalc.org/items/865
  • https://literature.hpcalc.org/items/866
• Rich Hawkes' "Nonpareil RPN HP-41 Calculator Build" - DIY hardware version of the HP-41.
• go41c calculator - Android App.
• Online HP-41C OWNER’S HANDBOOK AND PROGRAMMING GUIDE.