HP Saturn

"Saturn+" redirects here. For the video game magazine, see Paragon Publishing.

Saturn
Photo of HP48SX 1LT8 SoC die containing an embedded Saturn CPU
Photo of the exposed die of the HP 1LT8 Clarke SoC which contains the embedded Saturn microprocessor manufactured by HP for use in the HP 48SX
DesignerHewlett-Packard
BitsHybrid 64-bit GPR, 20-bit address bus, 4-bit datapath, 4-bit minimum word size
Introduced1984
Version"Level 2"
DesignCISC
TypeCombination of a load–store architecture with some exceptions which fall into the register–memory architecture family
EncodingVariable
BranchingCarry bit, "sticky" bit and other flag registers
EndiannessLittle-endian
Page sizeNo MMU or paging available
ExtensionsOnly extensions for emulated ARM-based "virtual" CPUs
OpenProprietary
PredecessorNut
Registers
Nine 64-bit GPR and "scratch" registers, two 20-bit "data pointer" registers and other miscellaneous registers
General-purposeFour 64-bit GPRs
Floating pointNo FPU registers
VectorNo vector registers

The Saturn family of 4-bit (datapath) microprocessors was developed by Hewlett-Packard in the 1980s first for the HP-71B handheld computer, released in 1984, and later for various HP calculators (starting with the HP-18C). It succeeded the Nut family of processors used in earlier calculators. The HP48SX and HP48S were the last models to use HP manufactured Saturn processors, later models used processors manufactured by NEC. The HP 49 series initially used the Saturn CPU until the NEC fab[nb 1] could no longer manufacture the processor for technical reasons in 2003. Starting with the HP 49g+ model in 2003, the calculators switched to a Samsung S3C2410 processor with an ARM920T core (part of the ARMv4T architecture) which ran an emulator of the Saturn hardware in software. In 2000, the HP 39G and HP 40G were the last calculators introduced based on the actual NEC fabricated Saturn hardware. The last calculators introduced to use the Saturn emulator were the HP 39gs, HP 40gs and HP 50g in 2006, as well as the 2007 revision of the hp 48gII. The HP 50g was the last calculator sold by HP using this emulator when it was discontinued in 2015 due to Samsung stopping production of the ARM processor on which it was based.[1][2][3]


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