The PDP-14 was a specialized computer from

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...

’s Industrial Products Group designed to replace industrial level relay controls for machinery and machine tools that performed repetitive tasks. It was specifically designed to function in the harsh electrical environment encountered in facilities where electric motors,

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...

s and arc welders were present, a significant adversity for normal computer electronics. The PDP-14 was specifically designed to be the first level of factory automation, functioning as a

programmable logic controller A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that ...

(PLC), through its ability to communicate with a standard DEC PDP-8

minicomputer A minicomputer, or colloquially mini, is a type of general-purpose computer mostly developed from the mid-1960s, built significantly smaller and sold at a much lower price than mainframe computers . By 21st century-standards however, a mini is ...

. The first unit was delivered in June 1969 and used to control a gear grinding machine. Its design as a "programmable machine controller" was patented in 1973. The PDP-14 was designed to process Boolean equations, usually expressed as “ ladder diagrams” and as such had a programmable read-only program (

PROM A promenade dance or prom is a formal dance party for graduating high school students at the end of the school year. Students participating in the prom will typically vote for a ''prom king'' and ''prom queen''. Other students may be honored ...

) memory. Programs were developed using a PDP-8 then tested using a direct connection to the PDP-14. The PDP-14 was put into a check out mode where instructions were provided by the PDP-8. Following checkout, the PDP-8 provided the instructions to be put into the PROM. Later versions (for example, the PDP-14/30, whose

instruction set In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...

was not

binary compatible Binary-code compatibility (binary compatible or object-code compatible) is a property of a computer system, meaning that it can run the same executable code, typically machine code for a general-purpose computer central processing unit (CPU), ...

) are based on

PDP-8 The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units sold during the model's lifetime. Its basic design follows the pi ...

physical packaging technology. There also was a PDP-14/35 and a lower cost/reduced I/O capability PDP-14/L.

Hardware

The

12-bit Before the widespread adoption of ASCII in the late 1960s, six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This also made it useful for storing a single decimal digit along with a si ...

PDP-14 could hold a maximum of 4K

words A word is a basic element of language that carries meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no consensus among linguists on its ...

for instructions. The system's configuration included a control unit and a number of external boxes: * I-boxes (BX14) were for discrete inputs from the controlled system. Up to 256 ''input'' sources could be addressed. * O-boxes (BY14) could control up to 255

actuator An actuator is a machine element, component of a machine that produces force, torque, or Displacement (geometry), displacement, when an electrical, Pneumatics, pneumatic or Hydraulic fluid, hydraulic input is supplied to it in a system (called an ...

s in the controlled system. * A-boxes could be filled with timer modules for controlling time-driven events or retentive storage modules which were not cleared with power loss. A-boxes occupied the output

address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve ...

along with the O-boxes. * S-boxes were essentially the same as the O-boxes, but there was no real output device. This enabled storing intermediate results. S-boxes also used the shared output address space. Hence the combined usable output address space of the ''O-boxes'', ''A-boxes'' and ''S-boxes'' was 255 or fewer.

Registers

The PDP-14 has seven 12-bit registers: * IR * PC1 & PC2 * MB * SPARE * INPUT and OUTPUT.

Instructions

Among the PDP-14 instructions were: * TRR to move data between some (but not all) of the registers TRansfer Register (contents). :::PC1 and SPARE have increment and decrement capabilities, permitting TRR to modify the value loaded into the register. * JMS JuMp to Subroutine at the address specified in the following 12-bit word, saving the return address in PC2 * JMR JuMp to RETURN from a subroutine, jumps to location saved in PC2. In effect, JMR is a TRR in which PC2 is transferred to PC1. * SKP SKiP is a TRR in which PC1 is incremented by 1. There were also TEST instructions (Test if something is ON or OFF) and SET instructions (SYN Set "Y" oN, SYF Set "Y" ofF).

Software

The original PDP-14 required that programming be done by DEC. Subsequently, software development for the PDP-14 was done on another system, the

. A PDP-8 program named SIM-14 allowed for simulating the PDP-14.

Photos

PDP-14

PDP-14's M740 Instruction decoder module

PDP-14's M745 PDP-8 Interface

References

External links

PDP-14 User's Manual

includes information about interfacing options
{{DEC hardware DEC computers Industrial_automation Industrial_computing Programmable_logic_controllers Computer-related introductions in 1973