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.

Overview

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.

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.

One notable feature that it shares with HP-17B and 27S is its capability to print to a thermal printer using infrared. The corresponding thermal printer is the HP-82240. It is the only calculator in the Pionner line capable of utilizing the graphics printing capability of the 82240, while other calculators in the line are limited to printing characters.

The HP-42s runs on SysRPL with many low level assembly language tweaks, and thus it supports many advanced features like the HP-28C series. For example, it treats complex values as an object taking up one stack level (instead of consuming two stacks on the HP-41C or having a separate imaginary stack as on the HP-15C). It also supports plotting to LCD with each pixel being individually addressable, and thus capable of drawing or plotting under program command. However unlike the 28C, it supports only 4 stack levels and does not have built-in plotting utilities, requiring the user to program their own.

Like other Pioneers, HP-42 ships with a debugger and self-test routine.

There are only two known bugs on the HP-42s.

Hardware Mods

Some users have reported success replacing the RAM chip of their HP-42s with up to 32KB of RAM and modifying the LC circuit to force the chip to run at twice the clock speed. However it must be noted due to the construction of Pioneers calculators, opening a HP-42s involves drilling heat-stakes and thus will irreversibly reduce its structural integrity.

Tricks

Master Reset: press Exit(On), Sigma+ and XEQ at the same time will reset the calculator to factory condition.

Machine Reset: press Exit(On) and Sqrt at the same time will trigger a Machine Reset which does not clear memory but interrupts any programs and puts the calculator into a usable state.

Debugger: press Exit(On) and LOG at the same time will put the calculator into a self test (as with 27S and 17B).