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simh.simh/linc/README.md
Lars Brinkhoff 68c9c5536f LINC: New emulator for the classic LINC. 
This emulates the classic LINC.  The design was settled in 1965,
increasing memory to 2048 words, and adding a Z register, an overflow
flag, and an interrupt facility.
2025-10-24 03:44:31 -10:00

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LINC emulator

This is an emulator for the classic LINC from 1965.

Devices

  • CPU - LINC processor. If throttled to 125k, approximately original speed.
  • CRT - CRT display. It can be disabled to run headless.
  • DPY - point-plotting display controller.
  • KBD - keyboard. Input comes from typing in the CRT window.
  • SAM - sampled analog inputs.
  • TAPE - four tape drives.
  • TTY - teletype.

LOAD

Software can be loaded into memory using the LOAD command. It will normally read a file with 16-bit little endian words; the most significant four bits of each word should be zero. If the -O switch is supplied, the input is a text file with octal numbers separated by whitespace.

To start reading from some particular position in the input file, add OFFSET= after the file name and supply a number in octal.

To specify where in the memory to put the data, add START= after the file name; the default is 0. To specify how many words to load, use LENGTH=; the default is to write until the end of memory.

A binary input file can be a tape image. A plain image is 512 blocks of 256 words each, totalling 262144 bytes. If the -E switch is used, there is a check for the extended image format that can have empty guard blocks at the beginning and the end. The last three words in the extended format specify the block size, first forward block number, and first reverse block number.

To state which tape block to start reading, add BLOCK= after the file name and supply an octal number in the range 0-777.

DO

The SIMH DO command has been modified. With arguments, it will execute a script file as normal. Without argument, it acts like the DO button on the LINC control panel. This executes one instruction from the left switches, with the right switches providing a second word if needed.

Tape drives

To mount a tape image file on drive n, type ATTACH TAPE<n> <file>. The plain or extended image format will be detected automatically. Tape drives are numbered 0, 1, 4, and 5.

The BOOT TAPEn command will act like entering a tape read command in the switches and starting the computer. The default is to read eight blocks starting at 300, and start from location 20. This is the conventional way to run LAP6. You can also add RDC= or RCG= to boot some particular blocks. START= can be used to specify the start address; it defaults to 20.

Keyboard

The keys 0-9, A-Z, and Space are mapped to their corresponding LINC keys. Enter is mapped to EOL, Delete and Backspace are mapped to DEL, and Shift is mapped to CASE. To type an upper case symbol on some key, press CASE, release it, and then type the key. For convenience, Alt is mapped to META.

The remaining keys are mapped thusly:

  • F1 is mapped to the pu key.
  • = is mapped to the i= key.
  • - and , are mapped to the -, key.
  • . is mapped to the `+. key.
  • \ is mapped to the |⊟ key.
  • [ and left backslash are mapped to the *[ key.

The remaining upper case symbols:

  • CASE A - ".
  • CASE B - „.
  • CASE C - <.
  • CASE D - >.
  • CASE E - ].
  • CASE F - *.
  • CASE G - :.
  • CASE Space - ?.

Teletype

The TTY device implmenents a teletype for printing output. When a file is attached, it will receive text decoded at 110 baud from relay output 0.

Some characters are translated by LAP6 from the LINC character to ASCII:

  • i to &
  • p to '
  • | to \
  • u to %
  • ⊟ to $
  • _ to @
  • " to ^
  • „ to ;

CPU

Registers:

  • P - Instruction location, 10 bits.
  • C - Current instruction, 12 bits.
  • S - Memory address, 12 bits - 11 for address, 1 for halfword select.
  • B - Memory data buffer, 12 bits.
  • A - Accumulator, 12 bits - one's complement.
  • Z - Various, 12 bits.
  • L - Link, 1 bit.
  • OVF - Overflow, 1 bit.
  • IBZ - Tape interblock zone, 1 bit.
  • ENI - Interrupt enabled, 1 bit.
  • PINFF - Pause Interrupt enabled, 1 bit.

Switches:

  • LSW - Left switches, 12 bits.
  • RSW - Right switches, 12 bits.
  • SSW - Sense switches, 6 bits.

Inputs:

  • INTREQ, Interrupt request, 1 bit.
  • R - Relays, 6 bits.
  • XL - External levels, 12 of 1 bit each.
  • SAM - Sampled analog inputs, 16 of 8 bits each; one's complement.

Documentation

Programming: https://bitsavers.org/pdf/washingtonUniversity/linc/Programming_the_LINC_Second_Edition_Jan69.pdf

Using the LAP6 operating system, text editor, assembler, tape filing system: https://bitsavers.org/pdf/washingtonUniversity/linc/LINC_Reference_Manuals/LINC_Vol_16_Section_3_LAP6_Handbook_May67.pdf