Saturn (microprocessor)
Encyclopedia
The Saturn family of microprocessor
s was developed by Hewlett-Packard
in the 1980s for programmable scientific calculators/microcomputers. The original Saturn chipset
was first used in the HP-71B
hand-held BASIC
computer, introduced in 1984. Later models of the family powered the popular HP-48 series
of calculators, among others. The replacement for the HP-48, the HP-49 series
initially used the Saturn CPU, but starting with the HP-49g+ model the calculators use ARM
CPUs that emulates the Saturn architecture.
-based; that is, the core unit of data is 4 bit
s, which can hold one binary-coded decimal
(BCD) digit.
The Saturn microprocessor is a hybrid 64-bit
/ 20-bit CPU
hardware-wise but acts like a 4-bit
processor in that it presents nibble
-based data to programs and uses a nibble-based addressing system. The main registers A, B, C, D, along with temp registers R0, R1, R2, R3, and R4 are a full 64-bits wide, but the data registers D0 & D1 are only 20-bit. External logical data fetches are transparently converted to 8-bit physical fetches. The processor has a 20-bit address bus
available to code but due to the presence of the high/low nibble selection bit, only 19 bits are available externally.
The Saturn has four general-purpose and five scratch registers
that are 64 bits wide. Data in the general-purpose registers can be accessed on nibble boundaries and used for calculations, whereas the scratch registers allow only load and store operations. The 64 bits (16 nibbles) can hold BCD-formatted coded floating point numbers composed of a Plus and minus signs
nibble, 12 mantissa
digits and a 3-digit exponent stored in 2's complement format (±499). The use of BCD instead of straight binary representation is advantageous for calculators as it avoids rounding
problems that occur on the binary/decimal conversion.
For optimum memory usage efficiency, the Saturn's addresses are also nibble-based. The three pointer registers (including the program counter
) and address
data paths are 20 bits wide, therefore the Saturn architecture can address 1 M nibbles = 512 K bytes. Beyond that size (e.g. in the 48GX), bank switching
is used.
In both the HP-48S/SX and G/GX series, the Saturn CPU core is integrated as part of a more complex integrated circuit
(IC) package. These packages have codenames inspired by the members of the Lewis and Clark Expedition
. The codename of the IC is Clarke in the S/SX, after William Clark, and Yorke in the G/GX, after Clark's manservant. The previous series of Saturn-based ICs were codenamed Lewis, after Meriwether Lewis
.
The CPU codenames are inspired by members of the Lewis and Clark Expedition
of 1804–1806, the first United States overland expedition to the Pacific coast
and back.
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s was developed by Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
in the 1980s for programmable scientific calculators/microcomputers. The original Saturn chipset
Chipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
was first used in the HP-71B
HP-71B
The HP-71B was a hand-held computer or calculator programmable in BASIC, made by Hewlett-Packard from 1984 to 1989.The HP-71B was known as the "supreme" hand-held calculator/computer of choice at the time for those seeking the ultimate in hand-held devices. It was particularly popular at The...
hand-held BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
computer, introduced in 1984. Later models of the family powered the popular HP-48 series
HP-48 series
The HP-48 is a series of graphing calculators using Reverse Polish notation and the RPL programming language, produced by Hewlett-Packard from 1990 until 2003. The series include the HP-48S, HP-48SX, HP-48G, HP-48GX, and HP-48G+, the G models being expanded and improved versions of the S models...
of calculators, among others. The replacement for the HP-48, the HP-49 series
HP-49 series
The HP 49G series are Hewlett-Packard manufactured graphing calculators. They are the successors of the popular HP-48 series.There are four calculators in the 49 series of HP graphing calculators...
initially used the Saturn CPU, but starting with the HP-49g+ model the calculators use ARM
ARM architecture
ARM is a 32-bit reduced instruction set computer instruction set architecture developed by ARM Holdings. It was named the Advanced RISC Machine, and before that, the Acorn RISC Machine. The ARM architecture is the most widely used 32-bit ISA in numbers produced...
CPUs that emulates the Saturn architecture.
Architecture
The Saturn architecture is nibbleNibble
In computing, a nibble is a four-bit aggregation, or half an octet...
-based; that is, the core unit of data is 4 bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s, which can hold one binary-coded decimal
Binary-coded decimal
In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...
(BCD) digit.
The Saturn microprocessor is a hybrid 64-bit
64-bit
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
/ 20-bit CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
hardware-wise but acts like a 4-bit
4-bit
The Intel 4004, the world's first commercially available single-chip microprocessor, was a 4-bit CPU. The F-14 Tomcat's Central Air Data Computer was created a year before the 4004, but its existence was classified by the United States Navy until 1997...
processor in that it presents nibble
Nibble
In computing, a nibble is a four-bit aggregation, or half an octet...
-based data to programs and uses a nibble-based addressing system. The main registers A, B, C, D, along with temp registers R0, R1, R2, R3, and R4 are a full 64-bits wide, but the data registers D0 & D1 are only 20-bit. External logical data fetches are transparently converted to 8-bit physical fetches. The processor has a 20-bit address bus
Address bus
An address bus is a computer bus that is used to specify a physical address. When a processor or DMA-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus...
available to code but due to the presence of the high/low nibble selection bit, only 19 bits are available externally.
The Saturn has four general-purpose and five scratch registers
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
that are 64 bits wide. Data in the general-purpose registers can be accessed on nibble boundaries and used for calculations, whereas the scratch registers allow only load and store operations. The 64 bits (16 nibbles) can hold BCD-formatted coded floating point numbers composed of a Plus and minus signs
Sign (mathematics)
In mathematics, the word sign refers to the property of being positive or negative. Every nonzero real number is either positive or negative, and therefore has a sign. Zero itself is signless, although in some contexts it makes sense to consider a signed zero...
nibble, 12 mantissa
Significand
The significand is part of a floating-point number, consisting of its significant digits. Depending on the interpretation of the exponent, the significand may represent an integer or a fraction.-Examples:...
digits and a 3-digit exponent stored in 2's complement format (±499). The use of BCD instead of straight binary representation is advantageous for calculators as it avoids rounding
Round-off error
A round-off error, also called rounding error, is the difference between the calculated approximation of a number and its exact mathematical value. Numerical analysis specifically tries to estimate this error when using approximation equations and/or algorithms, especially when using finitely many...
problems that occur on the binary/decimal conversion.
For optimum memory usage efficiency, the Saturn's addresses are also nibble-based. The three pointer registers (including the program counter
Program counter
The program counter , commonly called the instruction pointer in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register that indicates where the computer is in its instruction sequence...
) and address
Memory address
A digital computer's memory, more specifically main memory, consists of many memory locations, each having a memory address, a number, analogous to a street address, at which computer programs store and retrieve, machine code or data. Most application programs do not directly read and write to...
data paths are 20 bits wide, therefore the Saturn architecture can address 1 M nibbles = 512 K bytes. Beyond that size (e.g. in the 48GX), bank switching
Bank switching
Bank switching is a technique to increase the amount of usable memory beyond the amount directly addressable by the processor. It can be used to configure a system differently at different times; for example, a ROM required to start a system from diskette could be switched out when no longer...
is used.
In both the HP-48S/SX and G/GX series, the Saturn CPU core is integrated as part of a more complex integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
(IC) package. These packages have codenames inspired by the members of the Lewis and Clark Expedition
Lewis and Clark Expedition
The Lewis and Clark Expedition, or ″Corps of Discovery Expedition" was the first transcontinental expedition to the Pacific Coast by the United States. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William...
. The codename of the IC is Clarke in the S/SX, after William Clark, and Yorke in the G/GX, after Clark's manservant. The previous series of Saturn-based ICs were codenamed Lewis, after Meriwether Lewis
Meriwether Lewis
Meriwether Lewis was an American explorer, soldier, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition also known as the Corps of Discovery, with William Clark...
.
Chipsets and applications
The original Saturn CPU gave its name to the entire architecture. Later chips had their own code names:| CPU codename | Used in calculator models | Properties |
|---|---|---|
| Saturn | HP-71B HP-71B The HP-71B was a hand-held computer or calculator programmable in BASIC, made by Hewlett-Packard from 1984 to 1989.The HP-71B was known as the "supreme" hand-held calculator/computer of choice at the time for those seeking the ultimate in hand-held devices. It was particularly popular at The... , HP-18C HP-18C The HP-18C was a Hewlett-Packard business calculator which was quickly followed by the very similar but greatly improved HP-19B. The HP-18C was HP's first RPL-based calculator even though this model was not user programmable... , HP-28C |
640 kHz |
| Bert | HP-10B HP-10B The HP-10B is a student business calculator. The older model of this calculator proved to compete well with the higher end RPN HP-12C. The later-model HP-10B II is essentially a cosmetic upgrade offering the same overall functionality but actually reduces the available numbered-storage registers... , HP-20S HP-20S thumb|200px|HP 20SThe HP-20S is an algebraic programmable, member of Pioneer series of HP calculators produced from 1988 to 2003. It is similar to HP-21S... , HP-21S |
640 kHz, 10 KB ROM, 256 Bytes RAM, LCD driver |
| Sacajawea | HP-14B, HP-22S HP-22S The HP-22S is an electronic calculator from the Hewlett-Packard company which is algebraic and scientific. This calculator is comparable to the HP-32S. A solver was included instead of programming, but it was very well implemented... , HP-32S HP-32S - HP-32S :The HP-32S was a programmable RPN Scientific Calculator introduced by Hewlett-Packard in 1988 and discontinued in 1991. It continued the tradition of the HP-15C programmable RPN Scientific Calculator... , HP-32SII |
640 kHz, 16 KB ROM, 512 Bytes RAM, LCD driver |
| Lewis | HP-17B HP-17B Introduced on January 4, 1988, along with the HP-19B, HP-27S and the HP-28S. It was a simplified business model, like the 19B. There were two versions, the US one working in English only, and the international one with a choice of six languages. Code name: Trader.... , HP-19B HP-19B HP-19B, introduced on January 4, 1988, along with the HP-17B, HP-27S and the HP-28S, and replaced by the HP-19BII in January 1990, was a simplified Hewlett Packard business model calculator, like the 17B. It had a clamshell design, like the HP-18C, HP-28C, 28S.-External links:**... , HP-27S, HP-28S, HP-42S HP-42S The HP-42S is a programmable RPN Scientific hand held calculator introduced by Hewlett Packard in 1988. It has advanced functions suitable for applications in mathematics, linear algebra, statistical analysis, computer science and others.-HP-41 replacement:... |
1 MHz, 64 KB ROM, LCD driver, memory controller, IR control |
| Clarke | HP-48SX, HP-48S | 2 MHz, LCD controller, memory controller, UART Universal asynchronous receiver/transmitter A universal asynchronous receiver/transmitter, abbreviated UART , is a type of "asynchronous receiver/transmitter", a piece of computer hardware that translates data between parallel and serial forms. UARTs are commonly used in conjunction with communication standards such as EIA RS-232, RS-422 or... and IR control |
| Yorke | HP-48GX, HP-48G, HP-38G HP-38G The HP-38G is a programmable graphing calculator by Hewlett Packard. It was introduced in 1995 with a suggested retail price of 79.95 USD. HP credits a committee of eight high school, community college, and university teachers with assisting in the design of the calculator.The HP-38G, unlike most... , HP-39G HP-39g series HP-39g series calculators are the successors of HP-38G.There are five calculators in the 39 series of HP graphing calculators. These calculators have algebraic entry modes, and can perform numeric analysis together with varying degrees of symbolic calculation... , HP-49G |
3.68 MHz, LCD controller, memory controller, UART and IR control |
The CPU codenames are inspired by members of the Lewis and Clark Expedition
Lewis and Clark Expedition
The Lewis and Clark Expedition, or ″Corps of Discovery Expedition" was the first transcontinental expedition to the Pacific Coast by the United States. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William...
of 1804–1806, the first United States overland expedition to the Pacific coast
Pacific Coast
A country's Pacific coast is the part of its coast bordering the Pacific Ocean.-The Americas:Countries on the western side of the Americas have a Pacific coast as their western border.* Geography of Canada* Geography of Chile* Geography of Colombia...
and back.
External links
- A Guide to the Saturn Processor
- Summary information in the Museum of HP Calculators
- See also Paul CourbisPaul CourbisPaul Courbis , is a French programmer, mostly known for reverse engineering the HP-28 and then the HP-48 series of calculator, and writing multiple articles and books disclosing his findings...
's books which contain details about Saturn programming