CARDIAC

Code

Published

March 1, 2022

Modified

March 1, 2022

CARDboard Illustrative Aid to Computation…

…folded cardboard “computer”
…teaches how computers work
…originated from Bell Laboratories in 1969
Instruction manual (Internet Archive, CC-0)
Cf. article, Brian L. Stuart

Print out (Johan Von Konow, CC-BY-NC-SA)…

CARDIAC, left-hand CPU section, right-hand memory section

Components…

CPU section
- …sliders for….
  - …input
  - …accumulator sign
  - …instruction digits
Memory section
- …slider for output
- …100 memory locations
- …cardboard ladybug (aka program counter)

Architecture

Control unit …three part cycle

…fetch instruction to the instruction register (IR)
…increment program counter (PC)
…execute instruction register

Accumulator…

…4-digit number (overflow for numbers > 999)
ALU (arithmetic logic unit) supports…
- …addition
- …subtraction
- …decimal shifting (left/right)
…test for sign-negative or -positive

Memory…

…location stores a signed three-digit decimal number
…locations identified by numbers 00 through 99
- …00 always contains the value 001
- …99 always contains a value between 800 and 899

I/0…

…card reader (input) and a card writer (output)
…hold exactly one signed three-digit number
…read by way of the INP instruction

Instructions

Identified by an opcode (operation code)

Opcode	Mnemonic	Description
0	`INP`	read input …store to memory location
1	`CLA`	load content from memory location to accumulator
2	`ADD`	add accumulator to memory location …store to accumulator
3	`TAC`	acc. negative …operand address to PC …otherwise next instruction
4	`SFT`	shift accumulator
5	`OUT`	write content of memory location to output
6	`STO`	copy accumulator content to memory location
7	`SUB`	subtract content of memory location from accumulator
8	`JMP`	copy PC to address `99` …copy operand address to PC
9	`HRS`	halt (stop machine) …reset PC

…mnemonic abbreviations
Oxx …three-digit decimal numerals (non-negative)
- …opcode O left most digit
- …xx ..lower order digits …address/memory location

Anatomy of opcode decoding…

  ┌──── opcode (here for instruction INP)
  │
  034   ➡  read from input and store content to memory location 34
   ││
   └┴── address (here memory location 34)

  ┌──── opcode (here for instruction ADD)
  │
  235   ➡  add content from memory location 35 to accumulator
   ││
   └┴── address (here memory location 35)

Program

Simple addition of two numbers…

Line   Opcode    Description
──────────────────────────────
01     034       read input A
02     035       read input B
03     134       load input A to accumulator
04     235       add B to accumulator ...sum S in accumulator
05     636       store S
06     536       print S
07     900       halt

--- title: CARDIAC categories: - Code date: 2022/03/01 date-modified: 2022/03/01 --- CARDboard Illustrative Aid to Computation... * ...folded cardboard "computer" * ...teaches how computers work * ...originated from Bell Laboratories in 1969 * [Instruction manual](https://archive.org/details/CardiacCardboardIllustrativeAidToComputation) (Internet Archive, CC-0) * Cf. [article](https://www.cs.drexel.edu/~bls96/museum/cardiac.html), Brian L. Stuart [Print out](https://vonkonow.com/wordpress/cardiac-recreating-an-educational-paper-computer-from-1968/) (Johan Von Konow, CC-BY-NC-SA)... ![CARDIAC, left-hand CPU section, right-hand memory section](cardiac.webp) Components... * CPU section * ...sliders for.... * ...input * ...accumulator sign * ...instruction digits * Memory section * ...slider for output * ...100 memory locations * ...cardboard ladybug (aka program counter) ## Architecture Control unit ...three part cycle * ...fetch instruction to the **instruction register** (IR) * ...increment **program counter** (PC) * ...execute instruction register Accumulator... * ...4-digit number (overflow for numbers > 999) * ALU (arithmetic logic unit) supports... * ...addition * ...subtraction * ...decimal shifting (left/right) * ...test for sign-negative or -positive Memory... * ...location stores a signed three-digit decimal number * ...locations identified by numbers `00` through `99` * ...`00` always contains the value `001` * ...`99` always contains a value between 800 and 899 I/0... * ...card reader (input) and a card writer (output) * ...hold exactly one signed three-digit number * ...read by way of the `INP` instruction ![CARDIAC Control Unit and Accumulator](cardiac_control_unit.webp) ## Instructions Identified by an **opcode** (operation code) Opcode | Mnemonic | Description -------|----------|----------- 0 | `INP` | read input ...store to memory location 1 | `CLA` | load content from memory location to accumulator 2 | `ADD` | add accumulator to memory location ...store to accumulator 3 | `TAC` | acc. negative ...operand address to PC ...otherwise next instruction 4 | `SFT` | shift accumulator 5 | `OUT` | write content of memory location to output 6 | `STO` | copy accumulator content to memory location 7 | `SUB` | subtract content of memory location from accumulator 8 | `JMP` | copy PC to address `99` ...copy operand address to PC 9 | `HRS` | halt (stop machine) ...reset PC * ...mnemonic abbreviations * `Oxx` ...three-digit decimal numerals (non-negative) * ...opcode `O` left most digit * ...`xx` ..lower order digits ...address/memory location Anatomy of opcode decoding... ```txt ┌──── opcode (here for instruction INP) │ 034 ➡ read from input and store content to memory location 34 ││ └┴── address (here memory location 34) ``` ```txt ┌──── opcode (here for instruction ADD) │ 235 ➡ add content from memory location 35 to accumulator ││ └┴── address (here memory location 35) ``` ## Program Simple addition of two numbers... ```sh Line Opcode Description ────────────────────────────── 01 034 read input A 02 035 read input B 03 134 load input A to accumulator 04 235 add B to accumulator ...sum S in accumulator 05 636 store S 06 536 print S 07 900 halt ```