PDP-14

The PDP-14 was a specialized computer from Digital Equipment Corporation’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, solenoids 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 (PLC), through its ability to communicate with a standard DEC PDP-8 minicomputer.
U.S patent, #3,753,243 was issued on August 14, 1973 to Alan Ricketts, Allan Devault, Russel Doane, John Dumser, John Holzer and assigned to Digital Equipment Corp.
The PDP-14 was designed to process Boolean equations, usually expressed as “ladder diagrams” and as such had a programmable read-only program (PROM) 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 was not binary compatible) are based on PDP-8 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 PDP-14 could hold a maximum of 4K words for instructions. The system's configuration included a control unit and a number of external boxes:
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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: 
Instructions.
Among the PDP-14 instructions were:
In effect, JMR is actually a specific TRR in which PC2 is transferred to PC1. 
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 PDP-8. A PDP-8 
program named SIM-14 allowed for simulating the PDP-14.