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The HP-48 is a series of graphing calculators using Reverse Polish notation (RPN) and Reverse Polish Lisp (RPL), produced by Hewlett-Packard (HP) 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. The models with an X suffix have more onboard memory and are expandable via special RAM (memory expansion) and ROM (software application) cards. Models with a + suffix have more onboard memory only.
The hardware architecture developed for the HP-48 series became the basis for the HP-38G, with a simplified user interface and an infix input method, and the HP-49G with various software enhancements. Likewise, the hardware and software design of the HP-48 calculators are themselves strongly influenced by other calculators in the HP line, most of all by the HP-18 and HP-28 series.
The HP-48 series' Saturn microprocessor is an 8-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. 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.
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.
Common for all models
- CPU architecture: Saturn
- Screen resolution: 131×64 pixels
- Communication: serial port
- Data bus width: 8-bit (external)
- Maximum 4-bit-cell address width: 20 bits (leading to the address space shown next)
- Logical address space: 512 KB (or 1024 "kilo-nibbles" = 1 "mega-nibble")
- Maximum register size: 64 bit (both working and scratch registers)
- Available expansion card ports on X models: 2
- Expansion card pins: 40
- CPU clock frequency: 2 MHz
- CPU codename: Clarke
- On-board ROM: 256 KB
- On-board RAM: 32 KB (S) or 128 KB (SX)
- Maximum additional memory per expansion card: 128 KB
- CPU clock frequency: 4 MHz (variable according to the ambient temperature)
- CPU codename: Yorke
- On-board ROM: 512 KB
- On-board RAM: 32 KB (G) or 128 KB (G+/GX)
- Maximum additional memory for expansion card port 1: 128 KB
- Maximum additional memory for expansion card port 2: 4 MB (128 KB addressable at any given time via bank switching)
The HP-48 series of calculators support a stack-based programming language named Reverse Polish Lisp (RPL), a combination of Reverse Polish Notation (RPN) and Lisp. RPL adds the concepts of lists and functions to stack-based programming, allowing the programmer to pass unevaluated code as arguments to functions, or return unevaluated code from a function by leaving it on the stack.
- Byrne, Diana K., et al. (1994) "An Advanced Scientific Graphing Calculator: A concise treatment of design objectives, major engineering decisions, and the hardware/software of the HP-48G/GX, compared to the S/SX". Hewlett-Packard Journal 45 (4), 6–22.
- Mastracci, M. (1998)
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