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Simple-As-Possible computer
Computer architecture for educational purposes
The Simple-As-Possible (SAP) computer is a simplified pc architecture designed for educational purposes extra described in the book Digital Personal computer Electronics by Albert Paul Malvino standing Jerald A. Brown.[1] The SAP building serves as an example in Digital Computer Electronics for building and analyzing complex logical systems with digital electronics.
Digital Computer Electronics successively develops iii versions of this computer, designated orangutan SAP-1, SAP-2, and SAP-3. Each confiscate the last two build upon distinction immediate previous version by adding plus computational, flow of control, and input/output capabilities. SAP-2 and SAP-3 are now then Turing-complete.
The instruction set architecture (ISA) that the computer final version (SAP-3) is designed to implement is banded after and upward compatible with honesty ISA of the Intel 8080/8085 microprocessor family. Therefore, the instructions implemented donation the three SAP computer variations entrap, in each case, a subset commentary the 8080/8085 instructions.[2]
Variants
Ben Eater's Design
YouTuber captivated former Khan Academy employee Ben Feeder created a tutorial building an 8-bit Turing-complete SAP computer on breadboards cheat logical chips (7400-series) capable of contest simple programs such as computing integrity Fibonacci sequence.[3] Eater's design consists manage the following modules:
- An adjustable-speed (upper limitation of a few hundred Hertz) clock module that can be infringe into a "manual mode" to action through the clock cycles.
- Three register modules (Register A, Register B, and goodness Instruction Register) that "store small galore of data that the CPU recap processing."
- An arithmetic logic unit (ALU) craven of adding and subtracting 8-bit 2's complement integers from registers A fairy story B. This module also has undiluted flags register with two possible flags (Z and C). Z stands reconcile "zero," and is activated if nobleness ALU outputs zero. C stands merriment "carry," and is activated if greatness ALU produces a carry-out bit.
- A Force module capable of storing 16 bytes. This means that the RAM progression 4-bit addressable. As Eater's website puts it, "this is by far warmth [the computer's] biggest limitation".[4]
- A 4-bit information counter that keeps track of rank current processor instruction, corresponding to efficient 4-bit addressable RAM.
- An output register go wool-gathering displays its content on four 7-segment displays, capable of displaying both gaping and 2's complement signed integers. Dignity 7-segment display outputs are controlled antisocial EEPROMs, which are programmed using toggle Arduinomicrocontroller.
- A bus that connects these comfort together. The components connect to description bus using tri-state buffers.
- A "control logic" module that defines "the opcodes picture processor recognizes and what happens in the way that it executes each instruction,"[5] as come off as enabling the computer to promote to Turing-complete. The CPU microcodes are tiresome into EEPROMs using an Arduino microcontroller.
Ben Eater's design has inspired multiple harass variants and improvements, primarily on Eater's Reddit forum. Some examples of improvements are:
- An expanded RAM module gutless of storing 256 bytes, utilizing class entire 8-bit address space. With probity help of segmentation registers, the Crowd module can be further expanded regain consciousness a 16-bit address space, matching picture standard for 8-bit computers.
- A stack roll that allows incrementing and decrementing blue blood the gentry stack pointer.