er instruction, six lines of paper tape are read
and assembled in the In-Out Register to form a full computer word. For a
line to be recognized in this mode, the eighth hole must be punched;
i.e., lines with no eighth hole will be skipped over. The seventh hole
is ignored. The pattern of holes in the binary tape is arranged so as to
be easily interpreted visually in terms of machine instruction.

Read-In Mode

This is a special mode activated by the "Read-In" Switch on the Console.
It provides a means of entering programs which neither rely on read-in
programs in memory nor require a plug board. Pushing the "Read-In"
Switch starts the reader in the binary mode. The first group of six
lines and alternate succeeding groups of six lines are interpreted as
"Read-In" mode instructions. Even-numbered groups of 6 lines are data.
The "Read-In" mode instructions must be either "deposit in-out" (dio Y)
or "jump" (jmp Y). If the instruction is dio Y, the next group of six
binary lines will be stored in memory location Y and the reader
continues moving. If the instruction is jmp Y, the "Read-In" mode is
terminated and the computer will commence operation at the address of
the jump instruction.

PAPER TAPE PUNCH

The standard PDP-3 Paper Tape Punch has a nominal speed of 20 lines per
second. It can operate in either the alphanumeric mode or the binary
mode.

Alphanumeric Mode
ppa iot 5

For each In-Out Transfer instruction one line of tape is punched. In-Out
Register bit 35 conditions hole #1. Bit 34 conditions hole #2, etc. Bit
28 conditions hole #8.

Binary Mode
ppb iot 6

For each In-Out Transfer instruction one line of tape is punched. In-Out
Register bit five conditions hole #1. Bit four conditions hole #2, etc.
Bit zero conditions hole #6. Hole #7 is left blank. The #8 hole is
always punched in this mode.

TYPEWRITER

The Typewriter will operate in the input mode or the output mode.

Output Mode
tyo iot 3

For each In-Out Transfer instruction one character is typed. The
character is specified by the right six bits of the In-Out Register.

Input Mode
tyi iot 4

This operation is completely asynchronous and is therefore handled
differently than any of the preceding in-out operations.

When a Typewriter key is struck, Program Flag Number One is set. At the
same time the code for the struck key is presented to gates connected to
the right six bits of the In-Out Register. This