NP-41 Emulator (may be)

[Sylvain Cote]

Chris,

There are several things you need to know about the HP-41.

-> NUT processor instructions are 10 bits wide
-> RPN instructions are 8 bits wide

-> MCode (assembly) is the native language of the NUT processor
-> RPN language (FOCAL) is a user language intepreted by the routines contained in the 41OS

-> ROM is 10 bits wide
-> RAM is 56 bits wide (called registers, 1 register = 7 bytes = 56 bits)

-> NUT ALU registers are 56 bits wide

-> ROM is memory mapped
-> RAM is not memory mapped and treated like a peripheral (similar to SPI or I2C external memory)

-> ROM chips were initially build in 4K 10 bits word
-> RAM chips were initially build in 64 registers (64x7 bytes or 448 bytes)

-> ROM total addressable space is 64KB (16 pages of 4K word)
-> RAM total addressable space is 1024 registers (7KB) [less in reality]

-> Like Robert said before, the NUT processor support bank switching of up to 4 banks of 4K word at the page level giving a theoretical 256K word of ROM addressable code. [less in reality]

-> Devices like MLDL, Clonix-D, NoV-64 and others simulate 4K word ROM pages using EPROM, EEPROM, Flash, RAM or FRAM.

There is a lot more that can be said, but this is like the starting point.

Sylvain