STANDARD INPUT-OUTPUT
The PDP-3 is designed to accommodate a variety of input-output equipment. Standard input-output units include a Paper Tape Reader, Paper Tape Punch and an Electric Typewriter.
A single instruction, In-Out Transfer (see [Central Processor]), performs all in-out operations through the 36 bit In-Out Register. The address portion of this instruction specifies the in-out function. One bit of the instruction selects an in-out halt as required.
PAPER TAPE READER
The Paper Tape Reader of the PDP-3 is a photoelectric device capable of reading 300 lines per second. Six lines form the standard 36 bit word when reading binary punched eight hole tape. Five, six and seven hole tape may also be read.
The reader will operate in one of two basic modes or in a third special mode.
Alphanumeric Mode
rpa iot 1
In this mode, one line of tape is read for each In-Out Transfer. All eight holes of the line are read. The information is left in the right eight bits of the In-Out Register, the remainder of the register being left clear. The standard PDP alphanumeric paper tape code includes an odd parity bit which may be checked by the program. Tape of non-standard width would be read in this mode.