Programming instructions

CHAPTER 4

THE INTERFACE

ELECTRICAL CHARACTERISTICS

As explained in previous sections, the standard Interface contains the

Real-Time Connection, which can operate only with the Perforated-Tape

Reader, the Perforated-Tape Punch, and the Printer-Keyboard. The Real-

Time Option can operate with a variety of external devices over a wide

range of information handling rates. In this section the location of the

Real-Time Option, its electrical characteristics, and its connections to

input-output devices are presented.

Real -Time Option

A coordinate system locates modules and connectors in PDP-4 with a

four-place, alphanumeric code. Bays are numbered 1 and 2, panels are

lettered alphabetically downward, connectors or modules are numbered

left to right in the panels (blank spaces included), and terminals are let-

tered alphabetically downward on the connectors or modules. The Real-

Time Option is located in panels 2E, 2F, and 2H. Connections to external

control units are made through a cable connector in positions 2Jl-6.

DEVICE SELECTOR (LOCATION 2F6-25)

The standard Device Selector contains provisions for up to 20 selector

modules, each of which is a Pulse Amplifier, Type 4605. The amplifiers

are pulsed with standard DEC 4000 Series negative logic pulses which

can drive 18 units of base load.

Each module is wired to respond to one address code only (see example,

Figure 29). The 6-bit address portion of the iot instruction will therefor

pass only through the six-level AND gate of those modules wired to th

same combination of ones and zeros. The output of the AND gate enable

three AND gates to pass the common iot 1, 2, and 3 pulses. These pulse

are available at terminals E, H, and K, respectively, of modules 2F6-251