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cardiograph-computer/docs/mainframe-design.md

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[DRAFT] Design of the Cardiograph Mark I mainframe computer

The components of a Mark I are:

  • a CG 101 Central Processing Unit
  • a CG 102 Core Memory Unit
  • a CG 103 Print-Key-Punch
  • a CG 104 Matrix Display

Operator console

TBC TBC TBC

Basic controls

  • Power
  • Load
  • Run
  • Halt
  • 4 Sense Switches

Status lights

  • 8 Accumulator lights
  • 8 Address lights
  • 8 Data lights
  • 8 Instruction Pointer lights (review IP size?)
  • 8 Status Register lights

Debugging controls

  • Run Single Step
  • Memory Read
  • Memory Read Next
  • Memory Write
  • Memory Write Next

IO programming

Only one input or output device can be accessed at a time.

Reading data

  1. Use DEV xx to select input device xx
  2. Use INP yy to read one byte into memory at address yy

TODO: find a way to allow the input device to refuse to provide input

Writing data

  1. Use DEV xx to select output device xx
  2. Use OUT yy to write one byte from memory at address yy
  3. Use NXT xx to...
  • card punch: load a new card
  • printer: begin a new line (CR, LF)
  • display: begin a new line

Punched card format

FIXME:

  • Cards are punched in EBCDIC
  • EBCDIC data is translated into binary by the card reader/punch
  • Only columns 1-64 are used (for a maximum of 64 bytes of data per card)

Printer format

  • The printer format is the same as the card format
  • One line of printing is equivalent to one card
  • The printer can print up to 64 characters per line

Matrix display format

  • The display is a 5x5 grid of lights
  • Each light has 16 possible brightness levels (0 = off, 15 = maximum)
  • The display is written one line at a time
  • After the display is selected with DEV, writing begins on the top line
  • Writing wraps around and begins at the top again, if more than 5 lines are written

Device numbers

  1. card reader / typewriter
  2. card punch / line printer
  3. display

Print-Key-Punch configurations

A dial allows you to select which input device to connect to the CPU:

  1. none
  2. card reader
  3. keyboard

A similar dial selects the output device to connect:

  1. none
  2. card punch
  3. printer

Thus, this all-in-one device allows the following configurations:

printer card punch none
keyboard teletypewriter auto punch keypunch (offline)
card reader (keys + print) card duplicator (card reader)
none line printer (auto punch) (scrap metal)