HP 42S

The HP42s is a high-end RPN calculator in the HP Pioneer line. Launched in 1988, It was originally meant as a HP-41 replacement and thus had FOCAL compatibility, capable of running most HP-41 programs with little modification. However it was hampered in this role due to its lack of extensions and limited I/O capabilities, and was discontinued early (as compared to HP-17) in favor of HP-48 in 1995.

Hardware

HP42s used a silicon-on-sapphire Saturn architecture chip code-named "Lewis" with 64K of integral ROM and a RAM controller capable of addressing up to 64KB of memory, driving a 131x16 dot matrix display. 8KB of S-RAM is soldered on board and roughly 7000 Bytes are available to the user as program steps or registers.

Internally, the HP-42s is extremely similiar to both the HP-17B & BII, and HP-27S, with the exception of the lack of an extended ROM chip which on the 17 series contained international language & error message and on the 27S contained additional instructions. On the HP-42s, this position remains unsoldered. However, the instruction to jump to this memory location is still retained.

There are three major revisions of HP-42s: A, B and C respectively. Revision A and B have a plastic pane in front of the LCD whereas revision C has a recessed LCD display. Revision C is the most commonly seen variant today.

Software

The HP-42s runs on SysRPL with many low level assembly language