The Apollo Guidance Computer: Architecture and Operation Free

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The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC has a bit word length, with 15 data bits and one parity bit. Astronauts manually flew Project Gemini with control sticksbut computers flew The Apollo Guidance Computer: Architecture and Operation of Project Apollo except briefly during lunar landings. Laning Jr. They were connected via wire wrapand The Apollo Guidance Computer: Architecture and Operation wiring was then embedded in cast epoxy plastic. The computer had words of erasable magnetic-core memory and 36 kilowords [ clarification needed ] of read-only core rope memory. The CPU -internal bit word format was 14 bits of data, one overflow bit, and one sign bit ones' complement representation. It has an array of indicator lights, numeric displays, and a calculator -style keyboard. Commands were entered numerically, as two-digit numbers: Verband Noun. Verb described the type of action to be performed and Noun specified which data were The Apollo Guidance Computer: Architecture and Operation by the action specified by the Verb command. Each digit was displayed via a green high-voltage electroluminescent seven-segment display ; these were driven by electromechanical relayslimiting the update rate. Three five-digit signed numbers could also be displayed in octal or decimaland were typically used to display vectors such as space craft attitude or a required velocity change delta-V. Although data was stored internally in metric unitsthey were displayed as United States customary units. This calculator-style interface was the first of its kind. The command module The Apollo Guidance Computer: Architecture and Operation two DSKYs connected to its AGC: one located on the main instrument panel and a second located in the lower equipment bay near a sextant used for aligning the inertial guidance platform. The AGC timing reference came from a 2. The clock was divided by two to produce a four-phase 1. The 1. The master frequency was further divided through a scalerfirst by five using a ring counter to produce a This was then divided by two through 17 successive stages called F1 The F17 stage was used to intermittently run the AGC when it was operating in the standby mode. The AGC had four bit registers for general computational use, called the central registers :. There were also four locations in core memory, at addressesdubbed editing locations because whatever was stored there would emerge shifted or rotated by one bit position, except for one that shifted right The Apollo Guidance Computer: Architecture and Operation bit positions, to extract one of the seven-bit interpretive op. The instruction format used 3 bits for opcodeand 12 bits for address. The first eight, called basic instructionswere directly accessed by the 3-bit op. The final three were denoted as extracode instructions because they were accessed by performing a special type of TC instruction called EXTEND immediately before the instruction. Instructions were implemented in groups of 12 steps, called timing pulses. The timing pulses were named TP1 through TP Each set of 12 timing pulses was called an instruction subsequence. Simple instructions, such as TC, executed in a single subsequence of 12 pulses. More complex instructions required several The Apollo Guidance Computer: Architecture and Operation. The multiply instruction MP used 8 subsequences: an initial one called MP0followed by an MP1 subsequence which was repeated 6 times, and then terminated by an MP3 subsequence. This was reduced to 3 subsequences in Block II. Each timing pulse in a subsequence could trigger The Apollo Guidance Computer: Architecture and Operation to 5 control pulses. The control pulses were the signals which did the actual work of the instruction, such as reading the contents of a register onto the bus, or writing data from the bus into a register. Block I AGC memory was organized into 1 kiloword banks. The lowest bank bank 0 was erasable memory RAM. All banks above bank 0 were fixed memory ROM. Each AGC instruction had a bit address field. The lower bits addressed the memory inside each bank. Bits 11 and 12 selected the bank: 00 selected the erasable memory bank; 01 selected the lowest bank bank 1 of fixed memory; 10 selected the next one bank 2 ; and 11 selected the Bank register that could be used to select any bank above 2. Banks 1 and 2 were called fixed-fixed memory, because they were always available, regardless of the contents of the Bank register. Banks 3 and above were called fixed-switchable because the selected bank was determined by the bank register. The Block I AGC initially had 12 kilowords of fixed memory, but this was later increased to 24 kilowords. Block II had 36 kilowords of fixed memory and 2 kilowords of erasable memory. The AGC transferred data to and from memory through the G register in a process called the memory cycle. The memory cycle took 12 timing pulses The memory hardware retrieved the data word from memory at the address specified by the S register. Words from erasable memory were deposited into the G register by timing pulse 6 TP6 ; words from fixed memory were available by timing The Apollo Guidance Computer: Architecture and Operation 7. The retrieved memory word was then available in the G register for AGC access during timing pulses 7 through After timing pulse 10, the data in the G register was written back to memory. Instructions needing memory data had to access it during timing pulses If the AGC changed the memory word in the G register, the changed word was written back to memory after timing pulse In this way, data words cycled continuously from memory to the G register and then back again to memory. The lower 15 bits of each memory word held AGC instructions or data, with each word being protected by a 16th odd parity bit. This bit was set to 1 or 0 by a parity generator circuit so a count of the 1s in each memory word would always produce an odd number. A parity checking circuit tested the parity bit during each memory cycle; if the bit didn't match the expected value, the memory word was assumed to be corrupted and The Apollo Guidance Computer: Architecture and Operation parity alarm panel light was illuminated. The AGC responded to each interrupt by temporarily suspending the current program, executing a short interrupt service routine, and then resuming the interrupted program. The AGC also had 20 involuntary counters. The counters would increment, decrement, or shift in response to internal inputs. The increment Pincdecrement Mincor shift Shinc was handled by one subsequence of microinstructions inserted between any two regular instructions. Interrupts could be triggered when the counters overflowed. The AGC had a power-saving mode controlled by a standby allowed switch. This mode turned off the AGC power, except for the 2. In The Apollo Guidance Computer: Architecture and Operation mode, the AGC performed essential functions, checked the standby allowed switch, and, if still enabled, turned off the power and went back to sleep until The Apollo Guidance Computer: Architecture and Operation next F17 signal. To compensate, one of the functions performed by the AGC each time it awoke in the standby mode was to update the real time clock by 1. However, in practice, the AGC was left on during all phases of the mission and this feature was never used. The AGC had a bit read bus and a bit write bus. Data from central registers A, Q, Z, or LPor other internal registers could be gated onto the read bus with a control signal. The read bus connected to the write bus through a non-inverting buffer, so any data appearing The Apollo Guidance Computer: Architecture and Operation the read bus also appeared on the write bus. Other control signals could copy write bus data back into the registers. Data transfers worked like this: To move the address of the next instruction from The Apollo Guidance Computer: Architecture and Operation B register to the S register, an RB read B control signal was issued; this caused the address to move from register B to the read bus, and then to the write bus. A WS write S control signal moved the address from the write bus into the S register. Several registers could be read The Apollo Guidance Computer: Architecture and Operation the read bus simultaneously. When this occurred, data from each register was inclusive- OR ed onto the bus. This was accomplished by inverting both operands, performing a logical OR through the bus, and then inverting the result. The bulk of the software was on read-only rope memory and thus could not be changed in operation, [15] but some key parts of the software were stored in standard read-write magnetic-core memory and could be overwritten by the astronauts using the DSKY interface, as was done on Apollo The design principles developed for the AGC by MIT Instrumentation Laboratorydirected in late s by Charles Draperbecame foundational to software engineering —particularly for the design of more reliable systems that relied on asynchronous softwarepriority schedulingtesting, and human-in-the-loop decision capability. There was a simple real-time operating system designed by J. Halcombe Laning[17] consisting of the Execa batch job-scheduling using cooperative multi-tasking [18] and an interrupt -driven pre-emptive scheduler called the Waitlist which could schedule multiple timer-driven 'tasks'. The tasks were short threads of execution which could reschedule themselves for re-execution on the Waitlist, or could kick off a longer operation by starting a "job" with the Exec. The AGC also had a sophisticated software interpreter, developed by the MIT Instrumentation Laboratorythat implemented a virtual machine with more complex and capable pseudo-instructions than the native AGC. These instructions simplified the navigational programs. While the execution time of the pseudo-instructions was increased due to the need to interpret these instructions at runtime the interpreter provided many more instructions than AGC natively supported and the memory requirements were much lower than in the case of adding these instructions to the AGC native language which would require additional memory built into the computer at that time the memory capacity was very expensive. The average pseudo-instruction required about 24 ms to execute. The assembler and version control system, named YUL for an early prototype Christmas Computer[19] enforced proper transitions between native and interpreted code. A set of interrupt-driven user interface routines called Pinball provided keyboard and display services for the jobs and tasks running on the AGC. A rich set of user-accessible routines were provided to let the operator The Apollo Guidance Computer: Architecture and Operation display the contents of various memory locations in octal or decimal in groups of 1, 2, or 3 registers at a time. Monitor routines were provided so the operator could initiate a task to periodically redisplay the contents of certain memory locations. Jobs could be initiated. Many of the trajectory and guidance algorithms used were based on earlier work by Richard Battin. Details of these programs were implemented by a team under the direction of Margaret Hamilton. The Apollo Guidance Computer software influenced the design of SkylabSpace Shuttle and early fly-by-wire fighter aircraft systems. It retained the basic Block I architecture, but increased erasable memory from 1 to 2 kilowords. Fixed memory was expanded from 24 to 36 kilowords. The Block II version is the one that actually flew to the moon. Block I was used during the uncrewed Apollo 4 and 6 flights, and was on board the ill- fated Apollo 1. The decision to expand the memory and instruction set for Block II, but to retain the Block I's restrictive three-bit op. Various tricks were employed to squeeze in additional instructions, such as having special memory addresses which, when referenced, would implement a certain function. The Apollo Guidance Computer - Architecture and Operation | Frank O'Brien | Springer

See what's new with book lending at the Internet Archive. Uploaded by Mourad on August 27, Search icon An illustration of a magnifying glass. User icon An illustration of a person's head and chest. Sign up Log in. Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book. Books Video icon An illustration of two cells of a film strip. Video Audio icon An illustration of an audio speaker. Audio Software icon An illustration of a 3. Software Images icon An illustration of two photographs. Images Donate icon An illustration of a heart shape Donate Ellipses icon An illustration of text ellipses. EMBED for wordpress. Want more? Advanced embedding details, examples, and help! Publication date Usage Public Domain Mark 1. Much of the story of mankind's first voyage to the moon centers on its engineering. The sheer physical size of the vehicles and facilities not only dwarfed the previous. The Saturn V, with its. In the s, the Apollo Guidance Computer defined the state of the art in digital electronics. With so much time and effort already invested in an. As a result, the AGC grew The Apollo Guidance Computer: Architecture and Operation a newlyweds' house. Over time, the happy couple's family grows, and. Still, the house is quite functional, with each iteration representing the best ideas. Some aspects of the AGC were truly revolutionary for their time. The exclusive use of integrated. Other characteristics were like the newlyweds' house; the accumulated changes made the. This section discusses the key processor components. Importantly, the balance between power, flexibility and the. The Apollo Guidance Computer: Architecture and Operation final design is full of exceptions and special cases, but is especially notable. Understanding these constraints sheds. The second section is devoted to the operating system. The Executive. Complex programming logic used in the mission. A novel. This language was processed by a program called the Interpreter. Slow, but. The third and final section leaves the hardware and Executive behind to enter the world of mission. In turn, the execution. Properly covering each mission phase requires placing the AGC's operation into. Each Apollo mission built on the experiences of its predecessors, so there is no typical'' mission. Procedures and techniques reached their highest level of refinement in the. To discuss both. Also, despite its. Including material on programming techniques, especially necessary for. Finally, descriptions of the architectural The Apollo Guidance Computer: Architecture and Operation of the hardware and software. Apollo Guidance Computer: Architecture and Operation is intended to be the essential reference for. Both the design decisions and the compromises. Once defined, the spacecraft's operational capabilities became the principal driver in. There are no reviews yet. Be the first one to write a review. Apollo Guidance Computer - Wikipedia

Goodreads helps you keep track of books you want to read. Want to Read saving…. Want to Read Currently Reading Read. Other The Apollo Guidance Computer: Architecture and Operation. Enlarge cover. Error rating book. Refresh and try again. Open Preview See a Problem? Details if other :. Thanks for telling us about the problem. Return to Book Page. The technological marvel that facilitated the Apollo missions to the Moon was the on-board computer. In the s most computers filled an entire room, but the spacecraft's computer was required to be compact and low power. Although people today find it difficult to accept that it was possible to control a spacecraft using such a 'primitive' computer, it nevertheless had c The technological marvel that facilitated the Apollo missions to the Moon was the on-board computer. Although people today find it difficult to accept that it was possible to control a spacecraft using such a 'primitive' computer, it nevertheless had capabilities that are advanced even by today's standards. This is the first book to fully describe the Apollo guidance computer's architecture, instruction format and programs used by the astronauts. As a comprehensive account, it will span the disciplines of computer science, electrical and aerospace engineering. However, it will also be accessible to the 'space enthusiast'. In short, the intention is for this to be the definitive account of the Apollo guidance computer. Frank O'Brien's interest in the Apollo program began as a serious amateur historian. About 12 years ago, he began performing research and writing essays for the Apollo Lunar Surface Journal, and the Apollo Flight Journal. These Journals are generally considered the canonical online reference on the flights to the Moon. He was then asked to assist the curatorial staff in the creation of the Cradle of Aviation Museum, on Long Island, New York, where he helped prepare the Lunar Module The Apollo Guidance Computer: Architecture and Operation, a LM procedure trainer and an Apollo space suit for display. Get A Copy. Paperbackpages. More Details Other Editions 3. Friend Reviews. To see what your friends thought of this book, please sign up. To ask other readers questions about The Apollo Guidance Computerplease sign up. Be the first to ask a question about The Apollo Guidance Computer. Lists with This Book. Community Reviews. Showing Average rating 4. Rating details. More filters. Sort order. Jun 15, Torben Koch rated it it was amazing. Very exciting :. Aug 05, Brian Page rated it really liked it. But for the reader who comes to this book properly prepared, it is wonderful. The detail is nearly mind-boggling and thus, by properly prepared, I believe that for a reader to fully appreciate the content, they ought to have a significant understanding of computer architecture and operating system design. The Apollo program in its entirety was an enormously, almost unimaginably, complex assembly of technologies. Unfortunately, the need for nearly infinite cleverness by the programmers was the result of a self-inflicted wound. The original design specification called for bit addressability and only eight low-level instructions op codes. That it did not, and the techniques developed to overcome the architecture deficiencies, is what this book is all about. Jun 11, Peter Caron rated it The Apollo Guidance Computer: Architecture and Operation liked it Shelves: computertechnicalscience. I guess I never considered the obvious fact that rockets can be steered! This is a tough read but I found it worth the effort. The development of the navigation computers was as much about creative problem solving as it was about technology so, there is relevance for such work even today. Dec 27, Andy Cromer rated it really liked it. Frank O'Brien is a gifted engineer who introduces the Apollo Guidance Computer step by step or should I say register by register. After the core knowledge of the processing system the book switches to an overview of the program sequence and basics to guidance and navigation of the Apollo spacecraft. Overall a great book about the Apollo missions. Jan 14, Nikky rated it really liked it Shelves: default. If you've read books like Digital Apollo and wanted more information about the hardware and software that The Apollo Guidance Computer: Architecture and Operation into the Apollo Guidance Computer, this is the book for you. Thick with nuanced details about the inner workings of the AGC, you'll learn a lot about how a highly resilient and capable system was made in the late s. What you won't learn, however, is the design process or the writing of the software. It reads much like a technical manual for the AGC rather than a detailed history. Jul The Apollo Guidance Computer: Architecture and Operation, Greg Parrott rated it it was amazing. Though at times very dry, and a bit surprising at the number of typos, this book is a must read for engineers of all types. Before there were very many integrated circuit chips floating around, NASA took a gamble on them to meet the size, weight, and power requirements for getting men to the moon and back. Even back in the 's, engineers were having to more with less. A situation we still find today when "COGs" is often waved around by the bean counters. Aug 12, Matthew Wilson rated it it was amazing. Fascinating look, from both a computer engineering and computer science perspective, at The Apollo Guidance Computer: Architecture and Operation details of the computer that made the moon missions possible. Amazing what the engineers came up with, both working within the constraints of the available technology while also pushing the boundary of technology. Oct 13, Peter Joseph rated it it was amazing. A towering master work on what, admittedly is a fairly niche subject but if you want the real details on the computers that played a vital role in putting humans on the moon then read this. This book is more of a computer science text than a general historical book however, so beware of The Apollo Guidance Computer: Architecture and Operation. Sep 18, Neal Aggarwal rated it it was amazing. A fantastic trip down memory lane. Nov 21, Neal W rated it liked it. Bit esoteric for my taste. While I enjoy a technical read this one went a bit far over my head. Later chapters more of what I hoped for but a little short on analysis. 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