HP Saturn (microprocessor)

The processor family Saturn was developed by Hewlett -Packard in the 1980s for use in programmable calculators. The first Saturn processor 1984 used in the HP- 71B. Later models of the Saturn family were used in the popular HP -48 series.

Architecture

The architecture of the Saturn processor is nibble -based, that is, the core processes the data 4 -bit - wise and calculates internally using BCD.

The processor has four general -use registers for calculations and five copy registers which are all 64 bits wide. The data in the four arithmetic registers can be accessed nibble while the copy registers only support read and write access full register width. The 64 bits of an arithmetic register (16 nibble) to store the data in a special BCD - based floating - point format. The mantissa is represented by twelve BCD digits and the exponent with three BCD digits. This gives a maximum range of 10 ± 499 The use of BCD rather than binary fixed-point arithmetic reduces rounding errors when converting between binary and decimal number systems.

In order to ensure an efficient memory access, even this is nibble - based. The three existing pointer registers, including the program counter are 20-bit wide address, and each storage address in each case a nibble (4 bits, a BCD ). Thus the Saturn CPU can address Mebinibble 1, which corresponds to a memory size of 512 KB. Additional external memory, which goes beyond this address space (this is from the models HP- 48GX the case), is addressed by means of bank switching.

In the more recent HP calculators such as the HP - 49G , is not a Saturn processor more to use, but the ARM architecture. However, since extensive and well tested software is based on the Saturn processor architecture, is for not newly created system routines ( the firmware is relatively easy and secure interchangeable and continues to evolve ) on the ARM processor, the Saturn processor architecture emulated in software.

Chipset and applications

The original Saturn processor gave the entire architecture its name. Produced the processor family from NEC Corporation. Later processors had their own code names:

The processor code names are inspired by the members of the Lewis and Clark Expedition.

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